Here are 4 changes that I would make in PG
1 - Create a Team Stone. I raid in a group that is mostly blues, but has one red and one yellow. Needless to say, they are always penalized because at the end of a raid, the red/yellow team hardly does any damage, so they get fewer balls [despite the friendship levels]. So why not give them a Team Stone. At the next raid, they can use it, and so long as they are best friends with two trainers in that colour, they can change from red/yellow to blue. It's good for only one raid.
2 - Create a Franken Stone. This allows two 'mon in the same species to change characteristics. Specifically, if you start with one shiny with a 5% IV and a regular with a 85% IV, you can switch characteristics and end up with a 85% shiny and a 5% regular. This would count as a trade, so neither 'mon could be traded.
3 - Make trading fairer. I traded two dratini (between my two accounts) in the hopes that they would end up lucky. Both had 87% IV, exactly the same CP and identical movesets. The result - both received lower CP. One has an IV of 66 and the other an IV of 68. How is that possibly fair?! I can see the rationale of preventing someone with several accounts from creating an super account with the best 'mon... But the lucky lottery means that if you lose, not only have you wasted dust, but you also just lobotomized the patients. That seems very inconsistent with the rest of the game. I avoided saying "fair", but where else in the game do you get anything so skewed?
4 - Eliminate the shiny premium [relate it to IV]. If two trainers have the same 'mon [one shiny and one not], they should be able to trade as if it was a regular trade. Adding an exorbitant premium and then damaging the goods in transit [see above] just means that I will never trade a shiny in either direction. If I could [because the IVs of shiny are usually so low], I would just release the handful of unwanted shiny in my storage back into the wild so that a nearby friend could pick them up. Instead, why not relate the price of a trade to the IV? If you want to trade a 5% IV, go ahead, it's free. If you want to trade a 100% IV, that's going to be very expensive. That certainly seems a better way of doing things.
I have a few more changes that I'd like to see, but that's enough for today!