There is no automagic for 8k youtube videos, dear mr w1zzard. if you try playing an 8k youtube video, at least on my system, it uses av1 and i doesn't fall back to vp9. Since I have a gtx 1050, it uses my rather ancient cpu to do the decoding, which more or less brings my poor PC to a halt.
So please don't use the word magic without doing proper research please. AV1 decode is a necessity, not in the future, but now in fact.
I'm assuming that since this has dp 1.4a, it supports 8k TVs. There will be people having 8k TVs (please don't talk about practicality, people will buy them regardless they can tell the difference or not) and using this card in a htpc is a big nono based on the above.