And it likely won't come back because of the lack of support for 10bit channels needed for P3 displays. Jpeg2000 (Apple's alternative to webp) does.

Jpeg2000 has nothing to do with Apple per say. It's an open standard managed by the Joint Photographic Experts Group (part of ISO). Not even sure if Apple even participates in the group.

WebP on the other hand is a proprietary format developed by a single company, an implementation of which is made available under an Open Source License.

Jpeg2000 is sort of an open standard, but OSS doesn't and can't use it because it's patent-encumbered.

"It has always been a strong goal of the JPEG committee that its standards should be implementable in their baseline form without payment of royalty and license fees... The up and coming JPEG 2000 standard has been prepared along these lines, and agreement reached with over 20 large organizations holding many patents in this area to allow use of their intellectual property in connection with the standard without payment of license fees or royalties." (Wikipedia)

So yes it's patent-encumbered but no more patent-encumbered than WebP.

https://chromium.googlesource.com/webm/libwebp/+/master/PATE...

That statement is AFAIK now absent from the JPEG site.

On the positive side, it's now old enough that some key patents (e.g. arithmetic coding) have actually expired.