It seems like there should be a way to make Imperial city a separate area like any other zone with its own population caps except in the gated campaigns. The sewer entrance gank-fest would be eliminated if the entrances to IC were in another area such as Craglorn. I play DC so it seems underpopulated even when pop. Locked. Whenever I ask where all the DC are the reply is "in the sewers." I've been in the sewers and there seems to be plenty of enemy players there also but few DC.
Why not let the people who want to farm telvar and trophy vaults and duel have a place to do it without having to wait on players from their own faction who want to siege keeps. I think the developers at ZOS were afraid the interest in Cyrodiil would diminish completely if IC stood alone but I'm not seeing this to be the case, if anything it seems to be the other way around.
I can't imagine that Orsinium access will be dependent on anything other than your willingness to pay for it. IC should be the same.