In an absolute sense they're released, but these retail sets would be a new formulation of those previously released content, just like ATOH was released back in the 90's but this is a remake version. I don't think we can expect it will be two totally brand new creations that we've never heard of before.
I mean, what if it were? The Dwarf and Wizard Quest Packs (with new names and new re-imagined content)?
Would they give us two new hero collections that were for the Warlock and Druid? No, I don't think it will be that, but I suppose anything is possible.
The fact that these are going on Pre-Order to me shows that they are coming out soon, and how would they keep it completely secret with no teases prior to the unboxing up till now? It seems like it would be something we already know something about. An extensive new creation like ROTDM took a long time and they dripped the information to us prior to the "big reveal."
Another tactic that Encarmine loves is getting us thinking about other things right before the big reveal, a "swerve" if you will.

I'm sticking to my prediction that it's the Mythic content split into two of the smaller boxes, probably with some unpredictable bonus content.