I have heard about map converter tool from PawelS, that converts maps from AOW1 to AOW2SM. With some restrictions, but does.
So, I want to say that custom RMG could be easely done. What is even more easy, it is custom cities placer on already generated map.
What are benefits from it? More balanced cites distribution, no overlap, good amount of cities. Now in online games very often some players have no one city near capitol while others have three. So, they play a bit and often quit. To prevent overlap, big maps are selected that leads to long games that are never finished. Really, I do not understand, why these rmg is so unbalanced while it easy to place cities appropriate. And what is most easiest thing, is map validator that validate already generated map for balance among all players.
I have recently bad experience with wrong cities placement. One player was at underground just below under another, and had bad position. He lost soon, and the game was decided. Map validator could prevent it.