User blog comment:B214/Season 3 confirmed!!!!!!/@comment-25072311-20140617021856/@comment-9339850-20140617024810

You're assuming that if they pace the show out perfectly, which is subjective, and show all the material, not cutting out monologues and informational sections, which are the two things that always get pruned when an anime is adapted from a manga and even moreso a light novel. And even if they do it perfectly, and animate weekly as you say.. using the 8 seasons you've stated: 8Seasons X 12 Episodes a season = only 84 episodes.. so that is just over a year and a half of shows.... thats just not viable for an ongoing series. With that many episodes it'd be better to break them out every year or so.

Naruto, Bleach, and OnePiece get away with it because they blew up like a nuke when they first came out and are still profitable, regardless of how much people complain about filler. If DxD was to come out with the same amount of filler those series have (and it does have its own "filler" in the form of the couple of short stories that get mixed in) it would kill the series