Hi budweiser,
Whether there's too much focus on founding a religion, well, that is a matter of opinion of course. By the way, your idea is quite interesting, and has some historical flavor to it. I wonder if this mechanic is supported by the game already? Can one presently, using FireTuner or something like that, by fiat, add a second holy city for a religion? Does it work or do we crash the game? If the mechanic is already supported by the game engine and doesn't cause problems, do we increase our odds of successfully lobbying for developer action? Experience shows that developer hours tend to get scarce at this stage of a game's development cycle. Also, does your proposal constitute a replacement of the Byzantine UA, or an addition? Could they still enact one more belief than normal, and if so, would that affect the twin holy city as well?