There is already a few files in Data folder that lets you modify the game to some extent. These don't require much programming knowledge. So I assume gameplay modding will be a thing in future updates. There's already one Gameplay tag in the Workshop section.

If it was easy to add content mods I can upload my house-rule that I have played with for years (even in Pathfinder) and fixes Sorcerers in 3.5:

Give them access to their spells known at the same time as Wizards (every two levels, starting at third instead of fourth) but keep their spells per day at the same (so when they breach into their new spells their default per day is 0). This requires Sorcerers to have a high casting stat to actually cast spells at new levels, but severely limit them on quantity until the later levels.

Congrats, Sorcerers are no longer a whole level behind, and still cast exactly the same number of spells as normal. You're welcome. (I mean... they're still worse than Wizards, but at least they're not garbage.)

Modifying the file to make this work is seriously easy, but the hard part is getting automatic support and validation through Steam Workshop.

I hope that content mod support comes soon, because Pathfinder/3.5 has always been... almost balanced, and I would love to fix everything.