Not this again
I don't like wow but why would wow lose subs to a game that doesn't require subs and offers a different endgame experience? They will undoubtedly lose some as happens with every new game launch but most will play both because
A) they will no worse off financially
B) the games offer different endgame experiences.
There will be some clashes and some members Of both communities will be polarised and scream death on the rival but most will play both and enjoy it. As an example the 4 people I know who also plays MMO's are playing both, I'm the odd one in that I'm not