as a gold i can say that i'd love to play with golds only and leave these all silvers fighting each other. i should join the gold server then, but they are so empty that it's impossible to find a mission there. i think there are a lot of people with the same opinion because it doesn't matter where the silver is (in your or the enemy team), they don't play at the same level and we shouldn't be mixed. but there is a problem that even if one person joins a gold district, nothing changes because the rest of golds are still in the silver district (it is just their habit to choose it). the option of choosing lower threat district should be locked by the game so every gold joins gold district and most of them are happy because they play with players that are "at similar level" (imo they should add more threat levels btw, because gold≠gold, but this is an other problem, not to this thread).
tl;dr without interference of developers this problem is never gonna be fixed