IE6 still comprises of 17% of the market share, which is quite baffling.
I think it’s safe to say that most of the people using IE 6 are using it while at work, where their dinosaur IT chief makes the rules.
HTML 5 can only be superseded by another technology to present content on the web, so far there is no other alternative coming up (I’m not going to say the “f” word). So even though 2022 seems far off, I doubt what you implement today will become irrelevant then. If it does, hey just buy a new theme !