Don't forget that 4K Blu-Ray discs support HEVC encoding which is H.265 HEVC and 4K Blu-Ray players that support HEVC have been around since 2015/2016
H.266 VVC just came July 2020, so it's going to be a bit of time before we see Blu-Ray adopt it.
To give you an idea of how space efficient H.265 HEVC is over H.264 AVC is
For a given ~40 min 720p (1280x720) file encoded in the exact same video quality
H.264 AVC_ ~= 885 MiB
H.265 HEVC ~= 205 MiB ~= 76.84% savings in file size from H.264
H.266 VVC ~= 30-50% file size of the HEVC encoding.
Don't forget that Blu-Ray discs come in 25/50/100/128 GB standards in 1x/2x/3x/4x layers.
So you can encode ALOT of video onto Blu-Ray at whatever resolution you think is appropriate for a HD Remaster of Babylon 5.
Since Babylon 5 was filmed for SD resolutions, I wouldn't be surprised if they only stuck to HQ 1080p and shoved it onto 4K Blu-Ray to fit in as many episodes as possible onto a 4 layer disc.
H.266 VVC just came July 2020, so it's going to be a bit of time before we see Blu-Ray adopt it.
To give you an idea of how space efficient H.265 HEVC is over H.264 AVC is
For a given ~40 min 720p (1280x720) file encoded in the exact same video quality
H.264 AVC_ ~= 885 MiB
H.265 HEVC ~= 205 MiB ~= 76.84% savings in file size from H.264
H.266 VVC ~= 30-50% file size of the HEVC encoding.
Don't forget that Blu-Ray discs come in 25/50/100/128 GB standards in 1x/2x/3x/4x layers.
So you can encode ALOT of video onto Blu-Ray at whatever resolution you think is appropriate for a HD Remaster of Babylon 5.
Since Babylon 5 was filmed for SD resolutions, I wouldn't be surprised if they only stuck to HQ 1080p and shoved it onto 4K Blu-Ray to fit in as many episodes as possible onto a 4 layer disc.