The real answer is that the Doctor is limited to as many regenerations as the BBC can print money from. It would be insane to assume they would actually stop filming after twelve.
>I much prefer the Tom Baker years.
I adore Tom Baker, he's the Doctor I grew up with and his stories are what I always associate with "proper" Who, but let's be real, the serial format made stories as dull as dishwater a lot of the time, and more convoluted than necessary in order to pad out time.
I watched them on PBS in the USA late Saturday nights, and they strung them together, so a 4 serial episode would be almost 2 hours. That's what I miss. The stories have been compressed to fit in under 1 hour.
The rebooted Doctor Who seems too Americanized. Maybe it's the 1 hour story format. I much prefer the Tom Baker years.