Of course, we can't make an educated guess as to what's keeping Daniel Bryan out of the ring because there are factors involved other than the performer's own wishes. One poster in this forum says the WWE medical staff has cleared Daniel, while others say they haven't. Who really knows?
There is an interesting parallel to Rey Mysterio in all this. For all the time this guy was on the sidelines, do we really know the cause of it? I used to think it was Rey himself, refusing to come back until he was completely healthy .....and even then, maybe staying out longer.... because he could. Yet, after he was finally released from his WWE contract, he goes to another promotion and starts wrestling again. If any indication is provided by Rey's experience, WWE is playing it cautiously, either because they genuinely care about the performer......or because they're worried about the public relations aspect of letting a person go in the ring who shouldn't have been there and watching them get permanently hurt.
All this also applies to Daniel, making it virtually impossible to determine when, and if, he'll return. It could very well be WWE would grant him his release if he wants it, allowing him to wrestle somewhere else....yet he likes the WWE paycheck he receives for occasionally appearing on camera and getting the crowd all excited ('Yes!')