In the near future 16:9 8ks are going to be standard (too bad it won't be 16:10) but right now you can get a decent triple 4k monitor setup for half of what an 8k monitor costs.
IMO ultra-wide is great for productivity in a situational sense but it sucks for gaming and media consumption. Also getting proper support for ultra-wide to be standard is probably going to take another decade.
I think there's something to be said for each monitor being a separate entity. I think some people will still prefer multiple monitors over ultra-wide even when support for ultra-wide is a solved problem.
My personal setup now is a 28" 4k@60hz, a 32" 1440P@240hz as a primary and a 24" 1440p@144hz. I have my work computer, my desktop, a mac-mini, a switch, and a PS4 running off of them so having separate monitors is ideal for me.
Ultra-wides and super-ultrawides are cool, but IMO they aren't as practical yet.