Dalton being Rassilon creates a strange timey wimey issue with previous visits to the tomb of Rassilon (unless he's not the original Rassilon). I'd also like to point out that if we have The Bachelor, we also need The Associate and then maybe The Primary and The Secondary or The Elementary and The High Schooler. 😜
The Tenured Professor, The Fellow and The Emeritus/Emerita would like to have a word.
About Rassilon — first of all time travel. Second, isn't it implied that he died and was uploaded to the Matrix, but also maybe he lived on in some kind of astral form or whatever? I wouldn't be at all surprised if one of the founders of Time Lord society would be able to return, King Arthur style, when his world or time itself was in need of him.