Examination of HTTP2 effects on WordPress site speed.

Found this great multivariate test of how a wordpress site is affected by an HTTP2 upgrade. With & without caches.

https://css-tricks.com/http2-real-world-performance-test-analysis/

Best results were with http2 + cache, not surprisingly. But not many sites are using http2 yet so I'm wondering if anyone has seen negative performance? Or just general reasons not to use http2 ( it does require https ).