How hard would it be to port Gameboy titles to the PC Engine? Is it a similar language like the NES or would you have to start from scratch? If it's easily possible, Metroid 2 would be sweet in color.
Just a weird thought.
It's a totally different processor from the PCE's 6502-based architecture ... it's somewhere between an 8080 and a Z80.
The Gameboy hardware is pretty simple, but you're talking of a programming task that's more like the complexity of Aladar's Bubble Bobble port, or Old Rover's arcade ports ... or worse ... i.e. it'd have to be a real labor of love.
Oh ... and to make things even more obnoxious ... a lot of Gameboy games stored stuff compressed in ROM, which could add another layer of complexity onto everything.
Then you'd also need to find an artist willing to completely upgrade the graphics into color.
So ... it could happen, it just needs a programmer & artist who thinks that it'd be fun ... but don't hold your breath.