Pathfinder DSP only game?

[Efrate]

So after getting a chance to play and running only one occasional AP, been thinking about homebrewing a game in Golarion that uses only classes from DSP. I may need to research psionics because I have not dove into them pretty much at all, but I am quite familiar with Akashic and Path of War.

With no other classes existing in the world and the normal adventuring party paradigm thrown out the window, how would it effect the world, and how would monsters and CR need to be adjusted to fit?

Gurus can mostly replace the healing of clerics and be stand ins for faith based things, though external religion would be severely downplayed in most areas, more personal codes of faith. Same for druids likely. Psionics I am guessing replaces wizards/sorcerers, though viziers could do a reasonable impression in many ways including crafting all the magic gear needed.

My nebulous idea is very much cliche kung by movie, rival schools competing, then stuff hits the fan and various schools band into factions to combat A Thing. With some undecided, some on A Things side, and some fighting with you against it.

Monsters having Slas and such would be something they have because they are monsters, and that gives them stuff not directly ported from PC stuff. You have to have different ways to deal with their special monster abilities. You also may have to find a friendly monster to cast a certain spell, and have to earn it's trust so it would aid you. A significant portion of the opposition would be pc races in similar classes but specialized, so a pair of black Seraph focused warlords vs. Team PC showing you the power of their style. It would likely be very camp and over the top, but I think it has potential to be a ton of fun.

Any other massive changes on a setting scale anyone can think of that would need to address? And does it sound workable? I need to do the research on psionics, but I may even be able to leave that out.

[Dr_Dinosaur]

Psionics are a pretty easy stand in for arcane magic, with Akasha serving as the more mystical esotery of both druidic and monk powers (especially with the Trinity Veils). Martials are all now capable of pretty explosive damage numbers without much optimization, but there's Powers and a Zealot mission that can ressurect as needed.

I would personally allow Polymaths and Warpath Followers as weird unique situations but if you want all Paizo-style magic gone that's up to you

[Elricaltovilla]

It's very doable, and it sounds like you have a solid plan for implementation. All the DSP classes should give you a wide variety of options for play, with plenty of strong builds to choose from. You probably won't find it to be too different from running a regular campaign, honestly. I certainly didn't. If I have one piece of advice to give, it would be to focus on boosts and counters over strikes for any enemies that use maneuvers. That will help keep things from getting too out of hand.

[EisenKreutzer]

DSP psionics doesn't just have alternatives to wizards and sorcerers. The system has powerful frontline fighters and gishes, rogue-ish and ranged options as well as decent buffers and debuffers and even a healing class.

[Arkain]

If you want to include psionics, the authors also provived quite a bit of information about what to consider for psionic campaigns (https://libraryofmetzofitz.fandom.com/wiki/Psionic_Game_Mastery). I'd say that's worth a look at the very least.
Don't know much about akashic material to be honest, but running psionics without magic might become tricky in Golarion, as the deities seem to have had a bit of a direct influence there. Besides the whole Rovagug business, you've got places like Cheliax. Sure, you can maintain that as it is, Asmodeus worship and all, yet I wonder if that isn't a bit more believable, if he also exerts influence via power given to his clergy, making it all the more real. Then again, Black Seraph specialists wielding using "evil" power to fuel their maneuvers, so maybe just a question of refluffing. This might indeed be an interesting opportunity. Whereas you don't necessarily need gods, only faith, to gain divine spellcasting, scrapping it and other regular magic altogether makes gods, outsiders, dragons and such all the more weird if you just keep them as they are. They do these things that are often like powers, but not quite, in particular celestials with divine casting seem capable of things powers may have trouble replicating. If you add the occasional psychic magic using creature, you'd have some eerie similarities to psionics, but it's off. Investigating those things might be a nice plothook.