I don't like what the AI progress style of advancement would do on a 4X style game.
It makes everything move at the pace the player moves at. It removes all sense of having to surpass them, removes sense of competition and so on, and makes the AI completely passive. Actually, it's part of my lesser liked AI War design parts, that it's completely responsive to what you do. It fits with the theme though, so can't really be removed. About that 4X, there is no theme suggesting that they'd all wait for you. The AI already can't win (AFAIK)... so yeah, if the game's AI is designed for that, that sounds like a game I'd want to avoid.
About what I proposed, the whole point is to avoid problems associated with large cities, and to counter expansion hard, and to punish players for overexpanding. That's a heavy trends in current 4X because of a whole lot of reasons. The "main" one, IMO, is that not having any counter-balance for expansion leads, after a while, to a deterioratation of the mechanics into (boring) clicky grindfests by mid or end-game.