I think we'll continue to see creatures as pack-ins with deluxe figures (ie Dobby with Deluxe Lucius Malfoy). We could possibly see separate creatures from the new movie though as they're obviously the selling point for that movie. Newt will likely come with some, but some larger separate ones might be a possibility. I know in the podcast they said creatures we're really in their license agreement as separate releases, but neither was the new movie at that time either I think. So hopefully they've worked creature releases into the new contract. Just stay away from giant spiders. Give me dragons, three headed dogs, trolls, hippogriffs, and dementors a plenty, but no spiders
I'm not really sure what environments/dioramas they could do though. The mirror of Erised comes to mind. Great hall tables? The pensive? I'm not really sure what things would be small enough to do, but iconic/important enough to warrant a release. Quidditch hoops for those figures? I can think of plenty large accessories that could be made, but not many diorama pieces that would be doable and desirable.
I would like to see the Horcruxes and Deathly Hallows get releases with figures too. We got the wand, but nothing else yet - unless you could the invisibility cloak being invisible nothing
I think Asmus' build an orc idea is kind of cool. That could maybe be an option. Build a Death Eater perhaps? Collect a certain amount of figures that come with a few extra pieces to complete a Death Eater? I know they've said generic or background characters aren't really possible due to the figures' expense and salability but if you cost out some of those kind of characters as accessories they might be possible to do. A mask with one figure, a robe with another, wands with another, etc, etc. Its a great marketing gimmick for 6" figures but hasn't come to fruition in 1:6 scale yet - Asmus is still a WIP on that.