Hi riban,
This is probably exactly what I would be looking for.
I’m confused about what the snapshots and midi program changes you are referring to however.
I don’t fully understand (yet) how all this works. Plain English simple to store sounds 
The grid of buttons, grid size and different banks of buttons Yes!
Each stored sound should be capable of using different engines, ie DEXED marimba sound layered with a piano from another engine should be possible and easy. Split keyboard as well, I.e bass guitar sound left hand strings right hand, editable split point
Button colour might be assignable with midi channel? Your main piano sound in “bank 1” might be green, to correspond with Midi#1 assigned to your main controller, and drum sounds button blue for midi#2 assigned to drum pads on a smaller controller?
Labels and bank names editable
Maybe in “live performance” mode the 4 buttons along the bottom could select Banks and each bank screen could have up to 16 buttons? Configurable in menus?
Thanks
Andy Williss
VK5LA/VJ5Z
VK-QRP #752 GQRP #17085
Winkie, South Australia