[gribbly]

They won't remove support for HEVC/HEIF for quite some time, but they will support AV1 alongside them, why else would they join AOM at the top level (governing member) ?

This means AV1 will be the de facto next generation codec standard on the web as it will be supported by all browsers and all mobile devices, something HEVC never will.

[clouddrover]

HEIF itself is an image container format that supports a number of different image formats (like HEVC, AVC, and JPEG):

https://github.com/nokiatech/heif

Apple could and probably will add AV1 support to their HEIF implementation in the future.