I love Blizzard. Their playerbase is busy arguing about pandas and their dances. Then out of left field, Blizzard goes, "Hey guys, cross-realm zones. And they're seamless."
Ahh, Blizz, raising the bar for everyone else. Never stop.
I think we are seeing the beginning of the end of sharded servers. An end to the time when specific servers corresponded to specific pieces of hardware. Rumor has it that Blizzard basically operates a cloud of servers now, like Google, and the servers are all virtual.
I was wondering how they managed to put a million people in the Pandaria Beta with only four Beta servers.
I strongly suspect that Titan, Blizzard's next generation MMO, will be a single world for all players. Or possibly a world for each language and ruleset combination. And if Blizzard makes that truly seamless, with minimal or zero load screens, it will be an impressive feat.