Safari supports SPDY, I don't see why they wouldn't support HTTP2 at some point.
But that's a total red herring. HTTP2 won't help my phone load large image ads from ad networks faster. The connection overhead savings on the real site don't outweigh the giant image downloads either.
It doesn't matter what implementation you use, booting me away from content after the page already loaded is a HORRENDOUS usability mistake. Popover ads are terrible in the first place but waiting until I've read three paragraphs because the cell network is slow is moronic.
And it has nothing to do with Nitro. Safari is the base OS experience. Faster JS for 3rd party browsers wouldn't effect this as it's not an issue of JS speed. And you can't tell your customers "well if you want your experience to not suck download someone else's browser."