Only available in Australia so far.
https://www.jbhifi.com.au/movies-tv-shows/movies-tv-shows-on-sale/tv-sci-fi/seaquest-season-1/805839/
According to images posted on bluray.com, it's not just an upscale. The live action footage is in true HD.
I'm watching it now. It looks really, really good. The sets were extremely detailed. The VFX they did on Lightwave/Amiga Video Toaster holds up even today. I think having that hazy "ocean" filter really helped :p
Some scenes are upscaled (for example, at the end of Episode 1 Part 2), and the difference is jarring.
The one glaring thing is how low-resolution the (rear projected?) bridge screens and graphics were. Looks antiquated today, especially as I'm watching this on a 65" curved 4K TV :) BUT the graphics artists did a great job on the computer interfaces, since each computer terminal was showing believable information relevant to what's going on with the ship.
It basically looks like it was shot a few years ago, not 24 years ago...
Gallery:
http://imgur.com/a/l5Xu2
They did an AMAZING job.