I read about this earlier this morning. Like a lot of people, I've been concerned about Taker's health for quite a while. WrestleMania XXX is the worst he's looked, at least in my eyes; as I've said in other posts, WrestleMania XXX was the first time he really seemed like an "old man" to me.
If all the various reports I've read over the years are true, Taker has had a plethora of mobility issues concerning his shoulders, knees and hips. I've read that he's had multiple surgeries on his knees and hips and he underwent a shoulder surgery, not long after his last WM match with Triple H, that he'd been putting off for a long time. By the time he had the operation, the damage that'd been done was so extensive that the procedure really wasn't able to help. As a result, again according to the report I read, he probably would never regain full strength in that shoulder. I just can't remember if it was his left or right. Back in the early 2000s, I remember reading that Taker had suffered pretty badly torn groin muscles and had torn an abdominal muscle around the same time period. One reason why that stuck with me is that imagining a torn groin muscle just always gave me the creeps. Taker's getting older and the long term effects of the wear & tear of the business may simply be rearing its ugly head all the more.
Given that the streak is over, I'd say Taker's worked his last match. He's managed to pull it together the past several years to have some all time classic matches, though the physical price has been pretty high for him personally. If he's at a point in which he can't deliver matches at the level we've come to expect or, more importantly, the level that he himself expects, then he's done.