I don't know about normal Blu-Rays going anywhere, but UHD has clearly been a mess and a failure. Too many devices either can't play them or can't play them correctly. I'm sure this forum is probably filled with "from my cold dead hands" types, but I'll legitimately be surprised if there's a physical successor to 4K Blu-Ray. The future of extremely high quality audio/video might not be via Netflix streaming, but could instead just be via HQ digital downloads. Those can support multiple languages, legit HQ audio, and decent bitrates.