UHD bluray isn't really a new physical format. It's the exact same physical format as regular bluray. They didn't change a thing except move some previously optional parts of the bluray spec (like three layer discs, and 33GB per layer) to being compulsory.

I don't think we have ever seen something like it before. A new media format that breaks backwards compatibility, yet uses the exact same physical medium as the previous version. Some people did attempt it with HD movies on DVD, but the attempt failed so badly I don't think it even counts.

Its very existence was a very strong signal Bluray would be the last optical disc format. And the launch of the PS5 without a new optical confirmed it.