4-elements Monk

[Zuras]

Speaking as an interested DM here: what Xanathar's or EE spells are you most annoyed to miss out on? Magic Stone? Erupting Earth?

#1 would be Absorb Element.
#2 would be Warding Wind. That would be totally awesome to pick up at 6th level.

Wall of Water and Wall of Sand would also be fun if you could pick them up before 11th. As it is you don’t get enough disciplines for situational picks. Erupting Earth, Storm Sphere and Tidal Wave would also be nice thematically, if you wanted a quality AoE that doesn’t involve fire (following a single element theme).

Additionally, if the 4E monk could pick up Shape Water, Control Flames, Mold Earth and Gust along the way, that would help a lot at earlier levels where you otherwise run low on Ki and can’t do your elemental tricks.

When I looked at homebrewing a fix, I also considered the equivalent of Warlock invocations that let you cast spells once per Long Rest. For example, at 17th level you gain the ability to cast one of the four Investiture spells (chosen on level-up) for 6 ki once per LR.