Browsers already fully support 4:4:4 AVIF and are not going to regress on this, as it would be a huge compat issue.

It isn't clear whether AVIF hardware decoding will ever be an advantage, but for video formats, Firefox and Chrome already pick between hardware and software decoders to ensure the content plays correctly. Safari is much flakier here, but again, for images, they're not going to regress on 4:4:4 AVIF support.