As such, will we have a Doctor-lite episode in Series 8? And if so, will fans think it's an excuse to let Peter rest up a bit?
I think it's interesting that there haven't really been any obvious Doctor-lite episodes during the Matt Smith years. Certainly not when you compare it to Tennant, who made very minimal appearances in "Love & Monsters," "Blink," & "Turn Left." (He also spent most of "Fear Her" trapped in a child's drawing and was in bed for all but the last 20 minutes of "The Christmas Invasion.")
But when it comes to Smith, I don't recall any Doctor-lite episodes in Season 5. In Season 7, he was absent for the entire 1st half of "The Crimson Horror" but seemed to have a big role in the 2nd half of it. In Season 6, we had "The Girl Who Waited," which has deceptively little of the Doctor in it. He's a constant presence in the episode, because he's watching all of the events unfold on the monitor in the TARDIS, but it was probably a pretty short shooting schedule for Smith that week.
But then, Tennant pulled that trick too. He & Donna are barely in "The Stolen Earth." Most of that episode is spent on Rose, Martha, Wilf, and the Torchwood/Sarah Jane Adventures
And his age and extensive experience makes it less likely he'll be running off to Hollywood in a couple of years after he makes a name for himself
Certainly as such an established actor he probably won't have the same concerns about type-casting that most of the other Doctors had.
Wow. OK. Now we need to get Tennant & Capaldi to have a geek off! (Because there can be only one!)