The Zone Limit is actually the 'room size' for King's Row in our XMPP server.
For Atlas Park and Pocket D, there is no maximum amount of players. For other zones, the zone limit is able to be raised with early notice for an event or get-together past the cap of 30 users. (This includes multiple instances, as each instance takes up a 'player'.)
The 30 player limit is done on purpose: consider the number of maps in Paragon City, Rogue Isles and Praetoria altogether. With 30 users per map, the server's workload is manageable. And there's cheating: on all of the 100's of mission, encounter, and special maps, a set of 'shared' channels are used, so it's possible to hear someone in an Office building who is actually talking in the Summer Blockbuster Casino Heist set.
If the maximum is hit, players can move to Atlas Park or Pocket D if they want a place to see each other together "in person." If you have a one-time event, let me know and I'll see what I can do. For recurring events or weekly things, I can put it to Management for consideration, but no promises.