While BotB 2.0 is still young it's the best time to dream!! :D On the old engine we had remix compos, chiptune compos, 3xThemeChip and the ohcs. While we are still struggling to get all that renovated and working we can reflect on the things we've always talked about.
duels - a one on one battle
photomash - taking one or more photos or artworks supplied by BotBrs and making something new from them
pixels - giving a theme and/or limitations, BotBrs develop pixel art, kind of like on pixeljoint
minigames - probably already monopolized by minigame comp but maybe the communities could work together
adventure games - Adventure Game Studio is free and it would be interesting to see what teams/clans of BotBrs could come up with 1-3 months time