This sounds like it could be awesome for us F2Ps, could open up cross server hanging out, grouping and arenas!
If you group up with somebody from a different rule type (via RealID for example) and go into a cross-realm zone you’ll be on the ruleset for that player’s realm type. So, if you’re on a PvP realm and a friend joins your group from a PvE realm and enters a cross-realm zone, the group will be in one of the PvP realm clusters and will use the PvP realm ruleset.
If this works, people could plan events where players from all sorts of realms could Real-ID join existing groups on a PvP realm and get grouped in the same PvP zone. Could be a great tool for large-scale organised PvP events!