Was working on this yesterday- above is a mockup. But it's now kind of playable sort of! Check out some of this stuff...

Dynamic boxes- I've programmed it so I can just make a box of any size anywhere on screen.

Options selection where what's selected is based on the creation order of the options + supports vertical cursor movement as well.

Earlier gif before I added floating damage numbers- video of this stuff coming soon when it's more complete :3
You might wonder "you made a turn based battle system just for a mini game? Like only one battle?" and well... yeah :x but it wasn't as difficult as you might think. I already have a wait system built in(how all the cutscenes are done) so I used that as the basis for combat. I just had to program menus and a sort of new way of putting the text on screen but it wasn't terribly hard.
Now making a full rpg, with inventory, complicated menus, etc... would be a challenge. But I'm not stranger to doing that kind of stuff. It'd be a bit tough making an inventory system since GM studio doesn't have that built in(and doesn't support structs >_> which are perfect for things like inventory...) but I have ideas of how I'd do it.
But maybe someday Pizzass Games will be behind an RPG ;3 a lewd one probably.
-Velocirection, chief sexy officer of Pizzass Games