I was thinking of addition of vanity gear, that would let people show off their achievements in the game and give people some more goals to grind for.
Some ideas I've had:
Alpha Hunter Gear
Add a token that you would get each time you catch/KO an alpha, that people would get with the XP Candies.
Collecting these Tokens, you could exchange them to pieces of Alpha Hunter Gear.
There could even be like three different "tiers" of this gear, with color differences.
IE: Buying a tier 3 Alpha hunter hat, would unlock the possibility to buy tier 2 Alpha hunter hat, etc etc.
Shiny Hunter Gear
Pretty much the same idea than the Alpha Hunter Gear, but with shiny encounters.
Token is rewarded for every time you catch or KO a shiny, trade them for gear.
Gym Destroyer Gear
Tokens would be rewarded by every time you defeat a rematch with a gym leader
Elite 4 Destroyer Gear
Tokens would be rewarded every time you defeat an Elite 4 member OR beat the Champion.
etc. etc.
TL:DR
Main idea is to get untradeable achievement gear that you could buy with Tokens.
Lots of possibilities for different kind of achievements these gears could be tied to.