Not sure if it'd work out well, but give it a shot.
Certainly everything about all the countries, their provinces, trade, different values that are unique to Rome in all of the provinces, etc would have to be reworked.
And you might want to limit the whole "colonizing the Americas" thing, since the Romans et al were really, REALLY bad at making ships (they got their asses handed to them over and over again in naval battles, it was just stubborness that made them win eventually. And they had loads of trouble even building a boat that wouldn't sink in the non-mediterranean waters between Gaul and Brittania).
Certainly is a worthy project for an alternative mod, since AFAIK the Rome Improved Map Project is focused on being historical and adding more land where it is actually reasonable for it (like expanding the territory further down the nile and to the east). Would be fun to have WholeworldMap + Seriously increased tech-lines (possibly adding in EU3 stuff. Certainly you could create some delay between that, since Cataphracts etc could simulate knights) + Unlimited Time. Supercampaign!
..I wonder how big of a blob Ming would've turned into by the time ROME reached them. >_>
EDIT: Apparently they don't use the same colours for terrain and rivers, so either recolour that stuff, or change the meanings.