In my opinion, URF and ARURF aren't in the rotation enough. Only recently have they been releasing ARURF as a game mode that comes up "somewhat often". When Rotating Game Modes were released, anyway, URF was really only an April Fools joke that they brought back a few times as a fun, fast, and crazy game mode as an event or something.
Truly, I believe that RIOT has been slacking on the Rotating Game Mode (RGM) mechanic in general. I know they've announced that they won't be doing the whole RGM thing the same anymore, and that they would be focusing more on events, but I personally think they should go back to the way they used to be when they first released RGMs.. Put them on the weekend schedule again. Release them evenly, like on an actual rotation. Create item restrictions for each game mode (ex: take out warmogs for ascension or something along those lines..) and let people figure out their builds from there.
I agree that recently ARURF has been the more popular game mode that they've been releasing. I do miss Ascension, and Nexus Siege, and I did enjoy the 5v5 thresh battle mode, but I also love URF and ARURF more than any other LoL game mode I've played. So I'm a fan of them releasing it for play more often.
PS: I actually looked up "Rotating Game Mode LoL" on Google today in hopes of finding when the next RGM might be, and I found your post. I got halfway through writing this reply before seeing that ARURF was available to play again today. I was pleasantly surprised there was a RGM out right now :D 
