zitothebrave
Connoisseur of Minors
The master already has gotten around the 13 limit, so it's not exactly a hard and fast rule. It's been established that the clock can be reset by the Time Lord Council or whoever, and, why... look at how the Day of the Doctor ended... They were gonna have to deal with the doctor running out of regenerations as some point in the near future, so I can see Moffat wanting to go ahead and put his stamp on that.
The Master going past 13 was different but you're right the time lords in some form can reset the cycle or something like that. I'm sure they'll find a way around it, Doctor Who's grasp on continuity and logic is weak, but that's a healthy part of it's charm.