In my opinion it's quite obvious that it will be 3D was not only is it called construct 3
It's called Construct 3 because it's the follow up version after Construct 2 -- that's simple counting, not a reference to three dimensions, and no, it isn't at all misleading for that title to not be 3d.
We were already told it will be the same runtime engine with a new editor, so unless plans have changed it will definitely still be 2d.