Personally, I was always under the impression that the regen limit was statutory, not biological, based on things said here and there in the series, most noteworthy being the one time the council of the time lords offered the Master new regenerations if he did something for them. The twelve limit may well have been simply a population control measure -- and since there is no longer a population needing control, there is no need for a limit any more.
-- Bob
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Then the horns kicked in...
...and my shoes began to squeak.
-- Bob
---------
Then the horns kicked in...
...and my shoes began to squeak.