S6 starts April 23, the latest start date compared to previous seasons.
Well it starts at Easter, like it did last year. Late Easter, late start. ;)

That said, there is probably something in the fact that they've split the season up - it seems it tied in to what Moffat was writing, so they kileld two birds with one stone. And like I say below, it can't be easy being the headwriter, knowing how many people depend on you...