I was going to post only to say that production for Avengers: Infinity War has just announced that they'll start filming at the end of January (iirc on the 27th) to point out how that still doesn't seem the reason why TH hasn't announced anything, when the day brought a casting calls for the film with a list of the actors/actresses required and no TH!
http://www.moviecastingcall.org/open-casting-calls-for-avengers-infinity-war-and-untitled-avengers-movie/