I don't know what's stopping them doing a 1080p release though.
The Terrahawks bluray was done off a 16mm master if I remember right and it looked fine, although not *quite* as sharp as some.
So if they can find a 16mm or 35mm master, what's the hang up?
I doubt Japan cares enough to do so; I get the feeling they only did that piss-poor 2013 "Remaster" DVD just to try and milk some more money out of it.
I'm assuming Discotek got the masters from either Enoki Films or Fabulous Films. The masters on the US DVD are for the most part the same as the UK one but NTSC (so lower quality) but have some anomalies. Mainly the audio sounding a bit less clean and the opening credits are clumsily taken from Episode 8 (you can often see a single frame of the first scene of X-Bomber from that episode). Remember when the UK DVD was delayed from its original late 2008 release to early 2009? I have a feeling these were the masters that Fabulous Films originally edited before delaying the release to do further editing.
It makes me wish Network got the rights to Star Fleet instead of Fabulous Films; they did a Blu-Ray of "Space Patrol" last year and the prints were in worse condition than "Star Fleet"; they looked really good on it. Most of Fabulous Films releases' of older stuff are underwhelming like "Mysterious Cities of Gold". https://www.youtube.com/watch?v=p7us8T0b4kw
If you have that original release plus one of the Japanese ones, then you're gonna get everything that's probably on this blu-ray (apart from maybe new some extras).