Well now that I've caught up I can revisit this thread w/o being spoiled lol... And I still would like them to mention the limit, even knowing that it will be passed. I'm not sure about the transfer of energy from River or the universe reboot in Big Bang
having added anything to him, but the idea that the Time Lords rebooted the Master [who was already well past 12] means that it can definitely be done even if you stick w/the limit as being at least a concern.
It's more that I like the connections to classic Who, and however much it may have been a throwaway moment at the time, it's still there... I do like the idea of having him expect to really die and then be surprised when it works again. They could even have him speculate about why from the possibilities mentioned here w/o ever knowing the answer--and then not knowing if it'll work again. Sounds like a good hook into an arc about him being more careful, perhaps.