I wonder though how Smith would act towards one of the main obstacles of his past; that's the point with this Doctor - they never confront him with Gallifrey or with the Time War or with any of that sort. I think I may have heard him mention it once or twice, but he's never been allowed to convey that emotional load that Tennant had to frequently try to bring across. I bet Smith would be quite good at it too, if they just gave him that part of the Doctor's life too, as opposed to briskly dusting it off every now and then just because they remembered they need to mention that too once in a while.
I know I sound like I'm really knocking the scripting team, but it's true that it hasn't at all been the main point of attention for this Doctor's series yet, while it's a pretty big deal for the character to have to come to terms with - and worse - have to live with.
But yes, I'd like to see Simm return as the Master, though I wonder how they'd pull it off. While it's not quite clear what happened to him (that's some clever script-writing right there) in the end, it's pretty obvious he's now double-dead. I hope they wouldn't just resurrect him again - that would be lame. He'd have to make his way back some other way. Like when he was first reintroduced with Tennant, he was an old man and the audience has no idea how he got there or why that man was him - and neither did the old man. I like that mystery; not everything has to be explained - most of the time it's better if it isn't!
