There wouldn't be any point to upscaling TNG, DS9 or VOY and releasing them on Blu-Ray now. You will get the same result by simply playing your standard definition DVDs on a HDTV. (If the DVD player doesn't upscale, the HDTV will. Because if it didn't, you would only get a tiny postage stamp sized picture in the middle of the screen, surrounded by a huge black bar on all four sides.)
The whole point of a Blu-Ray release is to have it really be in HD.