The amusing thing is that HTTP/2 is mostly useful for sites that download vast numbers of tiny Javascript files for no really good reason. Like Google's sites.
Indeed, there is a reason most mapping libraries still support specifying multiple domains for tiles. It used to be common practice to setup a.tileserver.test, b.tileserver.test, c.tileserver.test even if they all pointed to the same IP/server just to get around the concurrent request limit in browsers.
