INNO has told us in the past that some buildings will return (the most popular ones). However, I would bet that set buildings will probably not come back around, for many reasons.
The buildings do seem to get recycled more than ever, so I think that the old sets will return (in hope of the new RR spell, should that ever make an appearance). I would love to know though, what Inno use to determine if a building was popular . I would think that if the majority of players obtained a certain building, then the demand for this going forward would be quite low (since most already have it), but I am sure this is just a clever way of saying "repeat the old stuff, that will save time and money making new stuff"
The old sets in the past have been (in my opinion) very weak, even with the full set bonus available, so I personally would be looking forward to the new sets.
Crystal ball time, - The last 2 sets from the last event, Market set and Owl set. I believe they will get nerfed before the year is out.