TNG, DS9 and Voyager will all get a blu ray release, it's inconceivable that they would pass up this chance. It's my bet that it will be some kind of upscaling though. Most people wont even know the difference anyway.
Oh, I think they will. And that's why it won't happen.
Why should Paramount go through all the trouble of releasing the shows on Blu-Ray without making them HD? Doing so would give exactly the same result as if the standard definition DVDs are played on a Blu-Ray player. (Remember, all HDTVs upscale all standard definition content anyway.) So why would they bother re-releasing the shows in a manner that will not give them anything new?