How about Alien 3. Alien 3 already has you searching around in an FPS enviorment, game with some sorta vehical stage?

Why not take three roms with the same mapper. Link them all together, and redo sprites, and backgrounds for each of the games.

The only change would be the score being kept from screen to screen. Think about it. You do a FPS stage, then a vehical stage, and final a action stage ( like mario ).

So it would be like rom 1 stage 2, score X then when we go to next stage it would be rom 3, stage 5 + score X + score keeps adding. Then to save score, it would be score = score
with initials, and that could be a forth rom ( program,  routine, etc ). Remember I came up with the idea first. , and some clown is going to program it.

This way a person could edit sprites of related mapper game, and then link the games as one game itself, removing extra data like title screen, in game art, etc.