Can't do the maths, 12 regenerations means 13 Doctors.
Susan: "Is he really..?"
1st Doctor: "Yes. Yes, I'm afraid so. Regeneration?"
5th Doctor: "Fourth."
1st Doctor: "Goodness me! So there are five of me now!"
The Valeyard is\was a potential distillation of the negative side of The Doctor, between his 12th & 13th Incarnations.
The Master - Extended his life by hi-jacking the body of Tremas, The High Council of Time Lords offered him a whole new regenerative life cycle to rescue The Doctor, re-engineered himself for a new regenerative lifecycle in the VNA's with outside help from the Tzun & then in the TVM he stole yet another body.
DWM also has him assume another body in The Glorious Dead.
The Scream of The Shalka has him existing in a cybernetic suit.
You may want to hide behind the sofa for the next line
RTD may or may not have him as being Mr S........
You can look now.
The Suns scaremongering\getting it wrong aside, each actor typically (Yes Eccleston I'm talking about you) assumes the role for 3 years\series, so that's aproximately another 9 series on top of the current planned 4th (barring accidents).
Apart from that I agree with the comments about ditching the kitchen sink\domestic angle, the gay agenda, lowest common denominator gags ie farting & deus ex machina rushed conclusions etc.
Instead keep the intelligent writers\scripts, humour, the current production values, tight pacing, but allow more intelligent story development with two parters with proper cliff hangers.
Thats my tuppence worth.