3 5x5s, one connected like a siamese cube(Whole UR connected to another cube), while the other one is joined at a 2x2 corner.
The 5x5s would be a cage or something, and allow the pieces to have blocks inside to move from a piece to another, like a 15 puzzle but in a form of a cube, piece or 2 would be empty
Then Have a mechanism such that it is fully functional(That would be insane if this really happens, unless we are living in another universe with different physics...
Reasons
I have always wanted a fully functionable Siamese cube
I love 5x5, although I love 7x7 more
I used to have a puzzle( 3x3x3, but not twisty puzzle) Where there is a different image on each side of the block, which moves about in the puzzle like 15 puzzle, but I lost it years ago
It would be insane