Whatever the developers' plans are, I think massive expansion of Mega City is quite necessary -- for several reasons.
So I would prefer to have one single world in the game, even if it's only a little part of the city, instead of three separated districts (Richland/Westview as one). Walking from International to Downtown and seeing how the city look changes would be much more exciting than just take the subway and see "ah, now I'm in DT, nice".
Not to forget all the historical locations that aren't in the game. OK, I have to say, I'm not really excited about how these places now look in the game (some of them are completely different from what we know from the movies), but still I'd like to see locations like Merovingian's "Le Vrai" restaurant or Seraph's teahouse in the game. I bet they are somewhere in the green part of the city. Of course, even more exciting would be to have places from ETM here. OK, the only way you can see the the power plant is watching the "maximum energy" posters, but others like the airport or the post-office would be very interesting to see in MxO.
Which leads me to the next point. I can't say everything inside of buildings looks the same, but it's still quite repetative and also a little too simple: the interior areas of Mega City roughly just consist of rooms at different floors, in large contrast to the complicated building structures of ETM. It's a little confusing, because what you see in ETM is really what you get to see in the real world; whereas the buildings in MxO really remind of the movies, because there, the clean and simple structures of the Matrix were supposed to be in contrast to the disorder and decay in the real world. I thought, it would be quite exciting, if the new districts wouldn't be just other versions and variations of the actual four, but would bring something new to the game. Like the freeway system in the north of Mega City, an industrial area with huge factories and power plants or some kind of travel district with airports (!) where planes or trains systems lead to other cities and stuff (there should be more than just one city in the Matrix, although I'm not quite sure). These areas could have much less typical apartment and office buidings and have a different structure than what we already know.
And the last one (I promise, it is!): We already saw real subway stations in the first movie and some other subway trains in the airport mission from ETM -- let alone, the sewer systems (not the worst level of ETM at all!!) -- and I think all these same-looking subway stations should be removed and replaced by a sort of underground city system. Would be pretty exciting. lol
So I think we'll just see what happens next.