I remember playing Pokemon Zeta/Omicron a while back and I believe the level cap was 120, but AT level 120 some Pokemon learned a new move-- Take my Magmortar, for example. When it hit level 120 it learned a move(I don't remember what it was called) that was basically a Blast Burn without a recharge. My point is, it'd be pretty interesting if you made new moves that Pokemon learned as they approached, or reached, the new level cap-- they don't necessarily have to be overpowered moves, just something new or even just a move that the Pokemon couldn't learn before, but can now. Either way, the level cap seems like a great idea for the "postgame shenanigans".