TNG, DS9 and VOY will be released on Blu-Ray sooner or later. There will be plenty of demand for those shows (well, maybe not VOY) from fans. If it doesn't appear on Blu-Ray, it might appear on Blu-Ray's successor technology. It will take some time to recomposite all the FX.
It would cost millions to redo all the effects in High definition. Millions
. I highly doubt they'll make back an investment of that much, unless they sell it to syndication much like TOS-R prior to a Blu ray release.