I think they should make a map that works sort of like the FPS capture and hold maps. Larger and less... Symmetrical. Yeah balancing a map that isn't symmetrical is hard, but not impossible. My mind keeps wandering back to some of the Battlefield 2 maps *v*.
Alternatively they could make a linear Dominion map with lots of side routes to make defending the points relatively challenging. By linear I don't mean training grounds linear, but a map that makes it extremely challenging (or enforced to be impossible) to take a point closer to the enemy spawn without having an owned point right beside it. Again, sort of a team fortresque idea, but it could be a lot of fun if implemented well, especially with LoL champs.
another idea could be an actual "King of the hill" map where there's only 1 large capture point and the capture radius would be large as well. Very challenging to defend overall, but there would always be battles going off in and around it. Again, pretty difficult to balance for the team on offense (how strong should the point turret be?), but I'm sure they could do it.