Television

Afaik HDMI hasn't been a bottleneck for movies in a long time. The 4k masters I had when I was working at a theater averaged around 100-200 megabits per second, which translated into movies that averaged around 200-300gb. Larger WORM (write-once, read-many) storage would potentially allow for master quality recordings to be produced for cinemaphiles.

While you might think there isn't enough demand for it, you might also not be aware that movies from back-catalogs come on hard drives. When your company has an outing to a movie theater where you all watch Elf together, that movie was likely originally on a hard drive (afaik only new releases get the luxury of being transferred via satellite). Instead of shipping spinning drives, they could ship data crystals (project silica) instead. This would have the side effect of potentially making the crystals reasonably priced for collectors and enthusiasts, allowing them to get the master quality version of their favorite movie(s).

For archival purposes, you want a lossless master so that new copies can be made from the original using any new codec that is later developed, whether that codec prioritizes quality, file size/bitrate, encoding/decoding cost, certain hardware optimizations, etc.

That way a 1995 film can be shown using a 2035 codec when the time is right, rather than relying on a 2035 encoding of a 2020 encoding of a 2000 digitization of a 1995 analog master.

The most recent HDMI versions are limited to 48Gbit/s, so you could fit almost 17s of a movie on a 100GB disk!

A lot more. A 4k disc has a bitrate of 128Mbps. Right now there are HDMI cables that can push 8Gbps and can be bought at Walmart.

The returns definitely are diminishing though. I am really struggling to see differences between 4k and 8k on an 80" screen at 6ft away – granted, I was looking at a floor model.

I think the real value is in archival though. If you have the true copy then you'll know you're not suffering any generational loss whenever you transcode the file. It'd also be nice to get the IMAX versions of movies with no loss of detail.