My understanding of the cross realm zones is that, should a zone be fairly empty, they'll 'share' that zone with other servers, so that you'll see other players and can team up if you'd like. You're not taken away from your server, or cut off from guild or friends, just opened up to some more players.
I am however surprised that they're so against server merges, but perhaps they foresaw many people returning to the game now the new expansion has landed, and therefore didn't wish to make any moves like that until they could gauge the numbers.
I should however say, that despite a few bugs and glitches, from being in game and actually talking to real players, the feeling is overwhelmingly positive.
Surely we should hold the opinions of players as more worthwhile than random ranty haters jumping on a passing bandwagon? (Not the OP, just the general level of WOW hate).
After all, this expansion was met with 'lolz kung fu panda, made for kids, gonna fail so hard, death of WOW'
Cataclysm was met with 'lolz gonna fail so hard', a similar tone was voiced with Wrath and the Burning Crusade. While I realise it's not growing any more, it's still doing just fine.
There's a lot of quality stuff being created by Blizzard's people for this game, but the trouble is (I dont know current numbers, but...) if you have 10 million players, and 1% don't like a feature, that's 100,000 players, many of whom will be voicing their opinions in game, and by forums and message boards and social media. It's tough to not see huge problems then, even tho, it's only 1%.
Lastly there's the 'lol it's all too easy' crowd, who seemed to think that Blizzard spending all their money on creating end game content that only a tiny fraction of their player base would ever see is a good move. All Blizzard have done is offer easier modes, so the content can be enjoyed by more people. If you want it epic hard, there's those options open to you, and you'll earn rewards consummate with your skill and effort.