User blog comment:B214/Question and Answers 6/@comment-3285616-20161121005601/@comment-9595671-20161123010527

I think every season's technically ended on one, in Season 1 Rias' mention of it not being the end of hearing about the engagement was technically a cliffhanger. In Season 2, the mention of a new house was a cliffhanger.

In a way, maybe cliffhangers are a way of saying "a chance for another season" in the DxD anime, if a 4th season didn't end on a cliffhanger, that could actually mean that's it and no 5th season.