ARAM's are probably the fastest games (unless you're counting bots), now that Dominion is gone. Ascension was a great bonus gametype and offers a significantly different experience from ARAM or Rift matches. A simple epic monster subbed in for Xerath and you could keep the crystal scar in circulation and offer a mad scramble style match.
I doubt they will release any permanent modes for a long time (if ever), since they are doing the game mode rotation that the community has been suggesting for such a long time. Ascension could possibly make a return though.
Riot's said repeatedly over the past few years that they have no plans to introduce another permanent map/mode. This isn't even that surprising considering how little support they provide(d) to the existing Alternate Modes of TT, ARAM, and Dominion. Rotating queue mitigates support issues by regularly scrapping each mode.
Ascension as a permanent queue would have similar issues as Dominion, mainly bug fixes and graphical problems. The Crystal Scar still desperately needs a facelift, and Riot unfortunately seems to think that SR-style gameplay is the only "legitimate" gameplay for MOBAs. It's unlikely that Riot would support any Alternate Modes enough for them to thrive.
