Dominion is a clever idea, but I think it's dead for a very specific reason that no one seems to talk about; it's impossible to balance the champions for multiple maps. Champions are conceptualized with SR in mind, and it takes more than tweaking numbers to make them interesting for dominion. Not all champs of course, but since not all champs translate well to that mode, it's always going to play second fiddle to SR.
I think dominion was conceptualized during a time when the theory for game balance was very different, and I don't think Riot will go back to it for any reason. I'll take it one step further, and say I HOPE they don't. It's isn't just because I love SR and want it to stay as healthy as possible; Dominion is also a clever idea and it deserves better than what Riot can offer it with a champion list specifically designed for another map.
It other words, Dominion can never thrive as a mode in LoL. It should be a different game. Just my opinion, of course, but there it is.