As far as new battle mechanics, I think seeing monotype battles implemented would be rad.
Most of my hopes/ideas come in the form of new/buffed abilities and moves -
Abilities:
1. SpA/SpDef versions for Intimidate, Guts, Weak Armor, etc
2. On-entry abilities for the terrain moves
3. On-entry hazard clearing
Moves:
1. Buffs to the terrain moves.
- Grassy gives Big Root style draining, increases grass-type Def/SpD
- Electric gives Zap Cannon 100% accuracy, gives elec status moves +1 Priority.
- Fairy -eh fairies are good enough. How about... Everything on the ground has a chance to be infatuated. That'd be infuriating.
2. Distribute Parting Shot, Topsy Turvy, Electrify, Parabolic Charge, etc to more Pokémon.
3. Give Charge Beam a 100% chance to raise SpA, lower power to 40, in line with Power-up Punch.
4. And the oft requested, Def boost for Ice types in Hail!
I'd love to see some status reworks:
1. Rework Confusion to use the higher attack stat and the corresponding defense rather than just Atk/Def. This would give some reason to actually use Flatter.
2. Freezing right now is basically a poorly distributed Sleep. What if, when using Ice Beam or whatever, the chance to freeze built up upon each hit. I think they'd have to decrease the chance to like 5% across the board. First hit has 5% chance, 2nd has 10%, 3rd is 15% and so on. Essentially, you're gradually cooling down the opponent to the point where they can't move. Obviously any fire moves used reset the counter. On that note, they could just turn it into a counter - hit with 3 ice attacks and you're frozen!