I see this topic has been brought up a lot and wanted to throw my 2 cents in in case this hasn’t been brought up before.
All instanced game modes should be cross-server (dungeons, 3v3, and OPR).
However, dungeons should be altered so that trading of non-consumables is not possible (unless they are set this way already, never tried), otherwise this creates the opportunity for some black market shenanigans popping up where different servers having different price points encourages people setting up trades to flip materials/craftables for profit.
OPRs should be setup in a way that either everyone in your OPR is from your server, or only your team is from your server, and I think there should be some kind of indication of what server you are facing off against. This will foster community within your server.
3v3s should be similar where the stipulation would be everyone on your team is from your server and it’s possible to face off against a set of 3s from either your server or another server. Also for 3v3s there should be an optional ranked mode as well as a group finder where you can signup with a specific roll. The roles being more varied than dungeon group finder: i.e. ranged dps, Support buffs, melee brawler, etc. (or just show a snapshot of their weapons could work I suppose). ALSO if ranked is implemented we need to be able to make team names similar to how Rocket League handles their ranked system.
My 2cents.