Unlike TNG, which shot both all of their live-action and all of their model photography on 35mm film, which made scanning the original elements possible, both DS9 and Voyager made extensive use of CGI for their visual effects, especially in the later seasons. Those visual effects were rendered in standard NTSC resolution, with a maximum of 525 scan lines of resolution per second, split between two interlaced video fields of 262.5 scan lines running at 60 fields per second. So, the original resolution remains far, far below what audiences used to today’s HD, and now UHD resolutions, are accustomed to. These VFX could be upscaled 5x, but they’d have no detail. The Starship Defiant would look like a fuzzy, grey blob.
If the VFX assets originally created for the shows could be acquired, which is a HUGE if, they could be reworked and re-rerendered in 2K resolution for Blu-ray, but even then, VFX artists would have to go in and add all kinds of upgrades to the original shots to make the ships, planets, weapons fire and explosions. look like they fit in with the gorgeous live-action photography. This would entail a number of artists working many, many long hours at considerable expense.
During the latter seasons of the TNG restoration, Mojo, one of the original, Emmy-Winning VFX artists on Voyager, who, at the time, was still in possession of many of the original DS9 and Voyager VFX assets, did a re-rendering VFX test on footage from “The Sacrifice of Angels.” The test really looked spectacular, and proved it could be done. But again, it would still take very talented VFX artists working long hours to accomplish the number of shots required for the episodes at great cost.
However, since then, I’ve heard many of these assets have been lost, either through drive failure, or simply the dumping of all the original data.
The only alternative would be to re-create all of the CG VFX shots from scratch, much the same way CBS Digital re-created TOS’ visual effects. But with the number of elements needed during DS9’s Dominion War arc, with sometimes hundreds of starships in combat, this could cost in the millions, if not tens of millions of dollars, depending on who was doing the VFX.