Well...the EB Team would have to be very careful to avoid something as extremely unhistorical as Massalia conquering all of Gaul which I fear is what a strong Greek faction in the south of Gaul would do. Nor can they be allowed to be wiped out after 10 years which is another very likely event.
If the EB team could get them to concentrate on just sticking to the coast then maybe it could work, but to be honest I feel that Massalia is the sort of city-state better represented as Eleutheroi, since they during EB´s timeframe never really tried nor could expand.
At most like a few regions west down the coast from Massalia, and even that was never really close to happening during EB´s timeframe. Had the game been set a hundred years earlier or more, then absolutely, Massalia would almost be a must, but now I think they´re better left out. Unless of course the EB team has some amazing plan for it.

Pergamon on the other hand, they certainly tried, could and did expanded a lot.