Of course the technologies are technically mutually exclusive, but the industry will never sell them as such, and as of now, 4k is rather firmly tied into the HDMI 2.0a specification standards and the bandwidth that operates on. 8k will be packaged with advanced levels of brightness, etc. There’s no way that you’ll see 4k and 8k sets sold with comparable specs in other departments. Perhaps a small overlap, but it won’t stay that way for long.
Sony claims their 8k protype is showing 10,000 nits, which maxes out the HDR spec. I saw it. It’s the best looking TV I’ve ever seen... bar none. It made their highly touted Z (which was the only TV capabable of over 1100 Nits during 2017) look washed and old. Limitations of HDR on the reproduction side, thus far, have been tied to processors and screen technologies. The industry is going to blow those issues up quickly.
Don’t underestimate the industry’s drive to mine money from the consumer pockets... as for media, look at the number to 4k UHD discs that have been upconverted. They will make it, whether real or not.
I forgot about Samsung and their QLED 8k TV. I believe they are claiming they will ship units before the end of this year, with the promise of a processor that can upconvert 4k to 8k. The process has started and won’t be long before before the very best models on the market will carry 8K resolution whether there’s true content or not.