Rotating Game Modes
Now I play a game called Runescape, some of you may be familiar, but that's not important. What is important though is that Runescape has about 20 or so mini-games, some of which are desolate because people don't play them any longer. To promote play in all mini-games, RS adds rotating incentives with "Spotlight Games." What if every weekend there was a random mode (including modes like Showdown, hexakill, poro king, Urf, etc) with a "spotlight" which became available and had bonus IP rewards for playing it.
This is purely a suggestion, as I think this is a good solution for the boring months between game modes.......