This page on the homebrewery.

So, I've decided to try something and post homebrew after only working on it for a few days; started this on Tuesday. This is less polished than my usual stuff. But my other homebrew going through my usual snail's pace means I'd otherwise have trouble filling my self-imposed upload schedule, so I'm posting this.

Anyway, the genasi are interesting thematically, but they don't have much fluff and they aren't actually very strong; if you're looking for a mechanically fitting option for a race then there's basically a better option no matter what. Half orcs typically get more than earth genasi, high elves get more use (and flexibilty) than fire genasi, kenku get generally more useful stats than air genasi, and hill dwarves get more than water genasi. So genasi are ignored by any sort of optimizer, and anyone looking for flavor has more lore and flavor to start with if they choose those listed examples anyway. So, I've rushed written some feats to both grant some flavor and add some mechanical concepts that are harder to get from other races in the PHB and VGtM.

Speaker with the Elements
prerequisite: Genasi

You are particularly in tune with the denizens of the elemental planes. You gain the following benefits:
  • Increase your Constitution score by 1, to a maximum of 20.
  • Whenever you make a Charisma check when interacting with Elementals, your proficiency bonus is doubled if it applies to the check.
  • You regain the use of your innate racial spell (Burning Hands, Create or Destroy Water, Levitate, or Pass Without Trace) at the end of a short rest.

A relatively generic half feat, based on one the subclass features of the Draconic Heritage Sorcerer subclass.

Friend of the Wind
prerequisite: Genasi (air genasi)

Your elemental powers are tied to an especially powerful storm or Djinn ancestor, allowing imporved ability to call on the wind for aid. You gain the following benefits:
  • You may treat any weapon lacking the heavy property as if it had the finesse property.
  • As a bonus action, you can channel the win to carry your weapons through the air, doubling the short range of your ranged weapon attacks until the end of your turn.
  • Whenever you take the dash action, you can dodge as a bonus action.

Airshaker Soul
prerequisite: Genasi (air genasi)

Your body thrums with thunderous power, which you can unleash on those around you. You gain the following benefits:
  • You learn the Thunderclap cantrip. Constitution is your spellcasting ability for this spell.
  • When you cast a spell, you can use a bonus action to bend the weave to unleash debilitating vibrations in the area affected by the spell. When you do so, one creature affected by the spell if deafened until the end of your next turn and cannot make opportunity attacks while deafened in this manner.
  • You gain resistance to thunder damage. As a bonus action, you can choose to lose this resistance, unleashing buffeting winds which cause ranged weapon attacks made against you to have disadvantage on the attack roll. By spending one minute in concentration (as if concentrating on a spell), you can suppress the winds and regain your resistance to thunder damage.

Friend of the Wind is meant for DEX based characters, particularly ranged ones. It might a be a bit too weak, actually, as Sharpshooter would probably be taken first, and the third benefit isn't very significant. Could be justified down to a half feat, perhaps. Otherwise I was thinking of adding some sort of limited fly speed; torn between a limited number of rounds per rest and a knockoff of the Starspawn feat from Lords of Madness.

Airshaker Soul on the other hand is specifically a caster bonus, particularly as you can attack a single creature next to you and escape without needing to take attacks of opportunity. Otherwise it could maybe use a ribbon.

Delver Descendant
prerequisite: Genasi (earth genasi)

Your genasi heritage comes from lower ranking dao who manage the mines of the great delve, or from those enslaved by the Yak-men of Zakhara, and are particularly adept at moving earth. You gain the following benefits:
  • While standing on earth or stone, you can cause the ground to ripple out from you in 10 foot radius. The ground in that area becomes difficult terrain until cleared. Each 5-foot-square portion of the area requires at least 1 minute to clear by hand. You can use this trait twice, and regain the ability to do so again at the end of a short or long rest.
  • When you take damage, you can use your reaction to reduce the damage you take by 1d4 + your Constitution Modifier. After you use this trait, you canít use it again until you finish a short or long rest.

Traveler of the Earth
prerequisite: Genasi (earth genasi)

Your connection to the plane of earth grants you a limited ability to earth walk. You can move through solid earth or stone as if it was air and without destabilizing it, but you canít end your movement there. If you do so, you are ejected to the nearest unoccupied space and you are stunned until the end of your next turn.

I feel like Delver Descendant needs to have the knockoff of Goliath racial feature replaced with something more appropriate. Perhaps a pseudo-rage that gives you resistances? It is mainly meant for a character on the front line, where rough terrain grants the most battlefield control. Otherwise I'd like to make it slightly more like Glacial Magic.

Traveler of the earth is a bit strong if anything; its a knockoff of one benefit the Investiture of Earth spell gives you, but doesn't require concentration. maybe instead grant a special 20 foot burrow speed instead?

Seething Skin
prerequisite: Genasi (fire genasi)

Your internal fire can burn out of control if you let it. As a bonus action, you can cause your body to become hot enough to ignite objects and harm creatures, or to cool back down to a manageable temperature. While in this state, you gain the following benefits:
  • Your touch attacks deal fire damage equal to 1d6 + your strength modifier.
  • At the start of each of your turns, you deal 1d6 fire damage to any creature grappling you or any creature grappled by you.
  • You can light unattended, flammable objects on fire by touching them.

Sight By Fire
prerequisite: Genasi (fire genasi)

Despite being only partially tied to the plane of fire, you are remarkably at home in the flames, not only unimpeded but able to command it to a limited extent.
  • Smoke and haze do not obscure your vision, and burning particles don't impede your breathing.
  • You gain immunity to nonmagical fire damage.
  • You learn the Control Flames cantrip.
  • You can cast the Daylight spell once, targeting yourself, and regain the ability to do so at the end of a long rest.

I'm questioning having Seething Skin deal more damage, to make it more useful for martial characters. Barbed hide is a half feat, for instance.

Similarly, Sight by Fire feels a bit weak. Maybe remove Daylight and make it a half feat? It is meant to apply more to casters.

Rushing Streamtide
prerequisite: Genasi (water genasi)

Your connection to the plane of water is strong enough for you to unleash blasts of water and turn partially to water yourself. You gain the following benefits:
  • Increase your Wisdom score by 1, to a maximum of 20.
  • You can expend one foot of swim speed to climb up to three feet downward and have advantage on checks made to keep your grip while climbing in this manner.
  • When you make an attack, you can use a free hand to make a melee weapon attack with a blast of water. Treat the water as having a 1d6 hit die and the reach property. The water you create in this manner dissipates immediately after the attack.

Glacial Magic
prerequisite: Genasi (water genasi)

You manage moderate moderate control of not only liquid water but also ice and snow. You gain the following benefits:
  • You can cast Armor of Agathys once, and regain the ability to do so at the end of a short or long rest.
  • You can move across difficult terrain created by ice or snow without spending extra movement.
  • You gain resistance to cold damage. As a bonus action, you can choose to lose this resistance, creating a 10-foot radius of frost, which moves with you. The frost is difficult terrain for creatures other than you. By spending one minute in concentration (as if concentrating on a spell), you can suppress the frost and regain your resistance to cold damage.

Finely, the water genasi feats. Rushing Streamtide is kind of generic, but should be most useful to WIS based casters and characters who would use a whip; whips have finesse but this is otherwise stronger and doesn't require a hand. Use with a component pouch if your DM is a stickler for the RAW rules on spells with somatic components.

Glacial Magic (like Delver Descendant) is more focused on martial characters. Thematically, you're meant to be unleashing the cold from within yourself, but keeping the resistance by default.