I know Cross Realm Outpost Rush has been discussed, but I would like to see that expanded to include expeditions, too. Low population servers can sometimes have difficulty find that “tank” or “healer” for an expedition.
However, I would disable trading inside the expedition with someone from a different server. If Fresh Start servers and Legacy servers run an expedition together, I can see the trade feature being abused to move gold, goods, or materials from one server to another without a character transfer. So, I would want to keep the servers intact, but allow people to play together.