I never said anything against the interface ;-)
Personally, I'm not a fan of separate packages for interfaces and the "primary" package they interface, some conditions of course do apply (i.e. FIG related interfaces). If we were to establish our own SessionInterface I'd rather see it shipped with the Session package. That's just nit-picking details and personal preference though in the long run. Especially since we already have 3 dozen repositories for the Framework, adding more just makes me cringe.
As for the timelines, I could be over-dramatizing or being realistic. But right now I'm seeing a lot of "safe" moves with code development and B/C. Even renaming String to StringHelper is being punted from a patch release to a minor release due to the very minimal potential of a B/C break in some third party's code. I'm not even going to push for v2 packages in the CMS until someone has a plan for 4.0 figured out, which the way things are going might not be anytime soon.