This was the response from Willy for haproxy: Yes, just discussed them with Piotr. Not really concerned in practice, maybe only the 1st one (1-byte win

This was the response from Willy for haproxy: Yes, just discussed them with Piotr. Not really concerned in practice, maybe only the 1st one (1-byte window increments) might have a measurable CPU impact but the rest is irrelevant to haproxy but could possibly harm some implementations depending how they are implemented of course. I use haproxy to provide http/2 and ALPN for my site, so if there is a PoC I will test it.