Apple will be using HEIF/HEVC and that's a lot of devices in one swoop. 500px is considering it. The various mobile-device connected sites like Instagram are probably thinking about it as well. These days adoption by individual users (like me sending a photo to you, or just posting up to this site, etc) may not be that important. The storage, quality and bandwidth reduction of HEIF/HEVC make it quite attractive to those outfits since they can gain financially from it. The end user of an iPhone might not even see it; it would all be done in the background. I suspect that the prevalence of online exchange and storage may drive its use more than previous attempts to move beyond JPEG.
But I expect this will be yet another opportunity missed by camera manufacturers, even though we'd get storage, quality, and wifi transmission benefits from it. I don't know that the processors could handle it, and of course they'd have to pay. But if you use RAW it won't matter.
Meanwhile, on macOS the beta of Graphic Converter has HEIF support for import, and will have export as well, probably by the release of 10.13.