We are going to stat testing with Windows Server 2016 and Sitecore shortly. Our Sitecore Server sites behind a reverse proxy so we will likey have to update the reverse proxy to 2016 also. We use a CDN although they currently do not support HTTP/2. I expect/hope to get some amount of increased performance by leveraging HTTP/2. Eventually though I suspect Sitecore will have to be updated to fully support all the features of HTTP/2, I can't imagaine all this will fall on IIS, this is based on my limited knowledge of HTTP/2, so don't judge.
I read in another Microsoft forum that older IIS versions (IIS 8.5 for example) might offer an update to IIS to support HTTP/2, although I am not holding my breath.