After seeing Pac-Man CE for the first time from the X-Box 360 Live Arcade, I began thinking about if it would be possible to recreate this on the original hardware. This soon changed from an "if" to a "how". By sacrificing a few things like the screen size, as well as visual effects, I believe it is fully achievable on the original 2Mhz Z80 cpu, with just a little bit of extra ROM space to hold new map data.
The thought is that it would be based on Pac-Man, but with various bits of code flown in from Ms.Pac. It would also have a replaced map render routine, to support drawing either half of the screen, as well as having stationary fruit that recharges a side with power pellets.
If the maps are set up such that the new map is inclusive of the old one, and just adds onto it, then there will be no issues with ghost weirdness - no ghosts stuck in walls and so on. For example it would not be necessary to change the ghost behaviour at all.