Just seen a comment on Cix from someone called systemcv about The Night of the Doctor:


There is a theory that, as The Doctor actually died this time without regenerating (and was apparently dead for quite some time - however long it took the Sisterhood to recover his body from the wreckage and then bring him back to life), all the rules have changed (again).

So, The War Doctor could actually be the first of a new set of 12 regenerations, which would make Matt Smith number 4 and Peter Capaldi number 5.