"We’ll also find out what makes his new companion so impossible and there’s a surprise that no one has got right so far, and one that will change the course of Who forever!"
I think it would be very difficult for anything to leave up to that. A lost Doctor would not change the course of Who for me. Nor would the older Doctors getting one of their younger incarnations to liven up. Both would be a very pleasant to see, but would not make me feel differently about the Doctor in any way.
To surprise me, it would have to turn out that the Doctor is dead, never escaped the Moment, his name is Ninth and his last incarnation was John Hurt. That kind of thing.
I suspect that Moffat is exaggerating, but I still hope (and fear) that he might be able to pull something that would actually surprise us. But I can think of nothing that could do it.