When I started playing Warcraft 3, there were no Pandas. When one made an appearance in the multiplayer and "founding of orgrimmar" parts, I thought it was funny and a nice hero to have in a party.
I did not think "hey, I want to have these things running all around my MMORPG"
Don't get me wrong, pandas are cute. The Chen's empty keg quest was a lovely piece of lore, but the whole reason they were interesting is because they were rare. I think you had the one in the bonus campaign in WC3 and the unlockable one during the rescue Illidan quest. They were rare, and because of that, they were interesting (as stated). Much like Jedi should have been in SWG, it should have been something you see rarely, but never en masse.
Now, since this is an MMORPG, there's no good way of limiting availability of something without people getting mad that they didn't have an opportunity to get it. I'm okay with it being unlockable through a time-intensive and difficult quest chain (as fewer people will have access to it), but tell me that on day 1 of this expansion we won't be inundated with panda DKs and panda monks everywhere. Imagine the DKs we had when WOTLK came out....every 2 minutes the faction leader yelled his "welcome the death knights" speech. It was annoying. Now we will have "welcome the brother panda" speech.
Don't get me started on the either or faction thing. At least most of the time when someone is coming you can roughly tell which side they are on. Now if you see a panda panda-ing down the road (wtf mount will be both asian and big enough to hold them? Or will it be the worgen solution?) you don't know if he's going to give you a bear hug or kill you with a bear hug.
And monks being healers? Seriously? Why not make them evasion-heavy tanks if you're going to do anything. Give them a stance or style or something that increases armor and stamina like a druid's bear form, and their evasion. That's much more monk-like than "my chi heals you" My opinion of course.
End of Rant, as you were