WEBP support has been added to the next version of Safari (14).
Good to hear. But that still means it'll still be 1½ years before enough users in the wild are on iOS 14 to make the change without breaking the sites for a large number of people. At least, from what I read, iOS upgrade adoption is very quick compared with other platforms.
WebP is something to look forward to on my company's internal projects, but externally we still have to support IE11, as it's still very widespread in the medical field, and I haven't seen the user numbers budge on that.
The space savings is quite nice for my bandwidth bills (my websites don't have video, so I estimate saving about 20% in bandwidth costs, or approximately $120/month across all of them).