U could limit the rules for list building like little cup in pokemon or the different competitive leagues. Restrict all leaders to having a centain number of total wounds (10 or something like that). Or a game where 25% of your army must be from every grand alliance (i actually would like to try this). Could also pick 12 leaders from your collection from any faction with point cost up to 200 points or something and roll 2d6 untill u get 5 leaders and do the same for units with a cost up to 200 points. Should get a random close to 2000 point army.
Could even go crazy and do something like a mtg draft with friends. Make a pile of random models/ units and everyone take turns to pick a thing they like until the pile runs out and go play a 2 vs 2. Could do all kinds of crazy things with open play.
Could even go crazier and do a capture the flag style game where u can only use leaders to capture the enemy flag and try to bring it home, when carrying the flag halve your movement stat and when defeated the flag drops at the slain model and the leader respawns at the base next turn (could make some crazy unreal tournament/warsong gulch style terrain for this). Time to go back to work now XD.
Edit: I think i'll do this Nozlocke thing when my wife decides she wants to restart an old pokemon game again. Sounds like fun. Might even do it in the new one this week.