The quality of a blu-ray disc is usually a magnitude better than the best streaming service. And a 4K blu-ray is years ahead of what streaming platforms even dream of.
Agreed on turning them digital. If you care about quality just remux them though, all a lossless codec is going to get you is a 10x larger file with the exact same output.
If only remuxing could get rid of the black bars that Blu-Rays include in the video stream because the spec only allows a small number of resolutions which surprisingly don't include any 21:10 ish aspect ratio common with movies.
Even just a convention for storing crop coordinates in metadata that players could automatically make use of would be godsent. Although a perfect solution would need to support varying this throughout the movie as some cunts (Nolan) like to use different aspect ratios for diffent shots.