This is an idea I also had back then for the DVD sets, but maybe for BluRay it even makes more sense:
The "8th Season" is pretty much a BluRay set containing TNG crossover episodes from the other Star Trek series (VOY, DS9 and ENT) - episodes, that contain TNG characters (actors reprising the TNG role) or are in direct context of a TNG story.
CBS could use this BluRay set to test the HD transfer of all the other Trek series and keep TNG fans interested in buying a BluRay set of Star Trek series they wouldnt probably buy, if it were just only VOY, DS9 or ENT (and vice versa, since it would bring pretty much fans of all series together in watching episodes of the other series in HD they otherwise wouldnt care about).
I would be massivly interested in such a project.
They are either going to convert DS9/Voyager or not. They are not going to convert a few TNG themed episodes in advance of that (IMO)
They are now hinting they WILL convert DS9.