It took 3 series to wrap up 11's storylines. Exploding Tardis,Silence,Trenzalore ect. So I reckon we will need to give 12 at least 2 or 3 series to sort out his. Think S8 will be a sort of getting to know you series. Don't know which villians he will be fighting but feel a bit sorry for them allready!. So maybe S9 and S 10 can try to fill in a few of the blanks. Galifrey for example. Is he ever going to go home and face the music so to speak ?. Could we see his original family and other timelords?. You could argue he owes them his life/lives. If they hadn't granted him a new set of regenerations he would be dead. You don't get something for nothing. Would 12 if he was able bring Galifrey back into our universe to pay his debt?. Even if it means possibly causing another time war?. Would be interesting to seee where they go with it. Hope the events of DOTD are not forgotten or ignored. Roll on August 23rd and 12's premiere.

I really, really hope not. It was an interesting idea to try the 'multi series arc' idea, but in my opinion one that ultimately did not play out well, with the audience being shown a set up each time, then not having it wrapped up and having to wait years never knowing for sure if the answers were going to come at all. Then after years of Moffat hinting that he had a grand plan, what actually happened was almost as if he'd forgot that he needed to answer everything and then shoved a few rushed lines into the final script, requiring Matt to quickly mumble through some lines of explanation as though they were unimportant, although the set up for questions we expected answers to had all been built up as big imperssive storylines.

In short, really hoping for an arc that is self contained within the series in which it starts and fully explained by the end of that series.

Although I liked the overarching storylines (I'm a sucker for the long-haul type stories), I have a feeling you are right. I don't think there's any danger of him leaving right now, but I doubt Moff is going to stay much longer. And if he does, it would be unfair to hand the reigns to someone else if you have already tied them down to your vision. It needs to be free for the next person to create their own storytelling, not be bogged down by catering to one already in full swing.

This could also be the case if it's sketchy to keep Capaldi. As he's one of the more high-profile actors to step into the role, it could be that he might have been able to wangle some kind of step-down clause into his contract, and you don't want to be halfway through a magnum opus to have to fudge the ending.