Idea of a bit of PvE fun! =D
Survival mode. Simple, right?
I think "murder bridge" is probably the best map for it, by default, but a mode where increasingly tough minions and AI champions come at a team of 3 (or 5) in waves would be a fun change of pace. No towers. Just a set of scaling melee minions to help stall the enemy minions briefly, so something like:
Your Team 3 Melee Minions that scale 3 players 2 ARAM-style health pads
Enemy Waves 3 Melee Minions 3 Caster Minions 3 Enemy AI Champions
Every 5th wave Includes 3 Cannon Minions and/or a Super Minion Every 10th wave includes a Dragon Every 20 waves spawns a Baron
Just some ideas... do whatever works, but gives us a some kind of mode like this. =)