They shouldn't monetize any "social" features in the game. This is really bad, and I'm really surprised in a negative way that Blizzard is doing something like that. If they keep doing that, they'll make more players quit.
OK to charge money for:
- remote auction house
- style items which don't increase character power (mounts, pets, ...)
- mobile armory (I know it's free, but they should rather make the chat stuff free than things like this)
- the game itself (monthly fee), helps ensure quality of servers and content updates
NOT OK to charge money for:
- remote guild/friends chat
- dungeon finder with friends
This should be common sense in a MMORPG.
I love WoW and Blizzard quality gameplay, but things like that really make me take a closer look at some upcoming alternatives like GW2.