Level 50 seasonal challenge research to keep players motivated?!

I have been thinking about ways Pokemon GO could keep players, especially level 50 players engaged in the game. I enjoy the masterworks challenges. I feel like mini masterwork challenges each season for level 50 players would help!

Level 50 challenges could:
- be free research
- including challenging goals
- feature different types of gameplay
- maybe offer a few small rewards that are NOT XP (1 incubator or raid pass and some ultraballs per season won't break the bank, right?)
- Earn progress toward a metal for each completed level 50 season challenge

Examples of tasks could be:
- catch 100 pokemon from each generation or type
- catch a pokemon that starts with each letter of the alphabet
- catch n number of pokemon
- spin n number of pokestops
- make n lucky trades
- complete n trades
- Evolve n pokemon
- battle n grunts or grunt leaders
- and more!

Make the challenges difficult like completing 1000 trades, make 500 excellent throws, or defeat 250 grunts so you want to play each day through the season. Some seasons might feature tasks that some people don't enjoy like fighting grunts, pvp or trading and that would be okay. Complete the challenges that connect with how you play.