Rumors and just that - it'd be too much work to redo all the effects of TNG for a blu-ray transfer.
Nah, TNG is a cash cow for CBS/Paramount. If the next film is as successful as Star Trek
(2009) was, I'd expect this project to move forward pretty quickly, as all parties involved attempt to cash in on the Trek namesake. It might take some time, but it'll happen.
Now, VOY and DS9, they'll probably never see proper Blu-Ray releases. Unfortunately.