I remember for what seemed like the longest time WB declined to give Babylon 5 the DVD treatment, citing that they perceived a lack of consumer interest in the series. It turned out that people had stopped buying the VHS tapes and laserdiscs because they had been led to believe that a DVD release was imminent.
Though I've heard about the next platform, I think it's a bad idea. It may only hasten the end of physical media by causing even more people to get frustrated and switch to bloody streaming.
I also wouldn't bank on ST (or a lot of TV shows for that matter) making it to the next platform. To redo TOS, they would have to re-render the CG effects all over again at a higher resolution (and that's assuming CBS Digital even saved their work; maybe they did, maybe they didn't). To redo TNG, they would have to rebuild the show from its photographic elements just as they're doing now for BluRay. And it still remains open whether DS9 or VOY will even get an HD remaster at all.
In general, a lot of what's on DVD will never make it to BluRay. And the same will go (even more so) for the next platform. I would say if you're been tempted to go HD on TOS, it's probably safe to assume BluRay is it. That or streaming.