In fact I’ve used a 100 foot fiber optic DisplayPort cable that I “just bought” on Amazon, admittedly for a LOT of money (like, I think it was about $100 USD, 3 years ago or so).

That's not actually such a bad price. I didn't know they even made these - cool!

Huh, I thought I had mine earlier. Mine was from May 2021. They were very very new and had very few reviews, and it was $56. For a 100' fiber optic cable that promised 8k60 and was light.

This cable is absurdly long. I have no idea how to coil it nicely. At my last place I had three stories, and would sometimes just dangle most of it down to the ground then wind it up from the roof.

I just wish they sold the transceivers separately from the fiber. Being able to use any random length of cheap off-the-shelf SMF/MMF fiber would be so much more convenient than having to get a custom one-off cable.

They exist for medium-speed HDMI (see for example [0]), but I haven't seen them for modern high-speed DP yet.

https://www.amazon.com/Converter-Extender-Transceiver-module...

You say it's a LOT, but it's about the same cost as a much much shorter USB 4.0 cable. (Granted, it also has to be able to carry 240W.)