They do not outsource their concept art and just say "go wild," it's pretty obvious in this image that they're previewing the fact that you can now use glamours, and also some new armor is being previewed on the WAR and BLM. Their concept art has always been fairly accurate. They have never drawn a wildly inaccurate player character using a weapon that obviously does not exist, in a manner that is obviously not possible, wearing equipment that is obviously not meant for the class.
What in the seven hells is going on? Normally I see dozen page threads speculating about things with way less in-your-face evidence, the reaction here and on Reddit has been surreal. I'm not necessarily saying we're getting it this patch, but that is definitely a dagger wielding thief-like character featured in concept art depicting player characters. And there is supporting evidence that this will be coming in the not too far future based on Yoshida's past conversations about classes and on Thancred's appearance in this patch.
Semantic?
Read the OP: To dispel the immediate knee-jerk reactions, keep in mind, GLA has not had a new dagger added to the game since 1.0 and an "end-game" style "unique" dagger like the one in this image has never been in the game. Additionally, GLA never holds their dagger backwards like this.