I personally think you guys should make it so you can message through servers. I don't mean make it a big chat, I mean like only being able to message your friends. Thank you and I hope you will take my suggestion into consideration.
It's not a bad idea all things considered. The game is definitely more fun when you are playing with friends. We do have a discord, so finding each other and talking to each other can always be done there, but not everyone uses it. In my opinion, it's an idea worth considering.
As much as I would love this, I don't think it's possible. If it was then the gyms would have been cross server. I wish they really find a way or something.