As soon as David became the new Doctor reporters were asking him how long he was going to stay in the role and the press was constantly speculating when his time would be up.
In 2007 this article ran in The Scotsman:
"Tennant is currently starring as the Time Lord in the third series of the new Doctor Who and the show will be back for series four - but Tennant has refused to reveal whether he will return in the lead role.
But undoubtedly there will soon come a time when fear of stagnation will lead Tennant to shuffle off his mortal coil in Dr Who's umpteenth regeneration. He will be a hard act to follow but somebody will have to do it - and the bookies are already taking bets on his successor.
Irish bookies Paddy Power make another Scot, Robert Carlyle, their 5-2 favourite for the role, with Liverpudlian actor David Morrisey of Viva Blackpool second best at 4-1. Jason Statham of Lock, Stock and Two Smoking Barrels is also at 4-1, but his ambitions lie in Hollywood.
Richard E Grant is quoted at 6-1 and the Withnail and I star would be an eccentric Doctor in the Tom Baker mould. So, too, would be Stephen Fry, a 10-1 shot.
Hard-man former footballer Vinnie Jones is 20-1 while Ricky Gervais is the outsider at 66s, though his stint in Night at the Museum showed he could handle any role.
But for an inspired piece of time-travel casting, why not try 10-1 shot John Simm, soon to finish his stint as Sam Tyler in the brilliant Life on Mars. He's handled going back 30 years just fine, so Simm could well be the man to take the Doctor character back and forth through the centuries." - April 8, 2007
Sound of Drums wouldn't air for another couple of months so John certainly got his time on Doctor Who just not as the Doctor. Richard E Grant has already been the Doctor in Scream of the Shalka and in the Red Nose Day sketch Curse of the Fatal Death. Also to be fair David Morrisey was the Doctor - for a least half an episode and Ricky Gervais got to be a Doctor Who villain in his series Extras.