Will it? I'm wondering how acceptable the actual texting will be. I can understand using the extra keys for control purposes above a standard controller (say, "F" brings up inventory or something), but how about the whole practice of using games like WOW as a virtual chat room? How will that type of thing fare?.
While it wont be as quick as having a full fledged keyboard, i'm pretty sure you can type fast enough with it. And having the comfort of not having to switch from keyboard to gamepad and vice versa every time you have to chat, will be worth the trade-off IMO.
The lack of a k+m option on the X360 was the only reason i could never see myself buying a MMO on the X360, mostly because, i don't see switching from gamepad to keyboard every time you have to type something as convenient.
With that add-on you dont have to do it, thus, better IMO. A even better solution would be full voice chat in MMO games ofc, but i just dont see how that would work.