I'd actually like something like Black Tower or White Treehollow instead of just another Battle Tower clone, but really proper frontier facilities are grossly under-appreciated imo.
So many people ignore the battle frontier or pass it off as boring/watered down competitive stuff but really that's what the Tower and its clones are to me. The other frontier facilities all add a twist to things that makes them a sort of game within the game. Sure, they involve battles, but they turn battling into a minigame in a sense. Some examples:
Battle Factory: You use rental Pokemon and when you defeat someone you're able to swap out one of your Pokemon.
Battle Pike: You go into one of three rooms, which can involve different events. Single, doubles, wild pokemon, healing, surprise status effect, or even nothing at all. You rely on a combination of luck and prediction based on hints given by NPCs.
Battle Arcade: Another luck involved facility, but here it's all battles with random effects. You might get weather effects or trick room, status affliction, be granted held items or berries etc. (or give your opponent held items/berries instead lol)
Battle Castle: As you win here, you earn CP, a special currency for use within the Battle Castle, by doing certain things in battle. You can use this currency for perks like held items, and even reducing the level of your opponent's pokemon.
Hell, there's even the Battle Palace where your Pokemon fight for themselves!