Tom Hiddleston was out promoting Crimson Peak and as always people were asking him about Loki. Loki was last seen in Thor: The Dark World, and judging by the cliffhanger of that film without spoiling it you would think it would be safe to say he would be back for its sequel Thor: Ragnarok.
However this might not be case. In an interview with ScreenRant he still has not heard from Marvel about their plans for the the film set to start filming late next year. On the matter he said “You know, I genuinely do not know. I wish there was something I could tell you. I haven’t spoken to anyone at Marvel for about two years. That universe is expanding at such a rate, so… your guess is as good as mine.
I mean, i’m interested to see what’s happened in the time between, I like to believe that actually he runs Asgard pretty well. The trains run on time and he keeps the streets clean. (Laughter) I honestly don’t know”.
Although it is surprising I that Hiddleston hasn’t heard anything yet, its likely more the case that Marvel haven’t started planning Thor: Ragnarok yet. It would be very surprising if Loki isn’t in either that film or Avengers: Infinity War Parts 1 or 2.