User blog comment:Cloverfield monster/Should we get Dr. Doom as a Cinematic Universe villain?/@comment-1895174-20140216184333/@comment-1895174-20140216233149

They're still being built up though. Their appearance in The Avengers opened the book, not finish it. Especially with GotG coming up this year and possibly a Capt./Ms. Marvel movie at some point. Thanos is their end boss, after all.