Huet

I want to second this. We have seen a real drop in our search rankings and Google consistently knocks us for not using next gen formatting. If you need to post lots of pictures on your site like us (travel site) you can reduce size and optimize jpegs only so far and they are still a lot of data. 

I develop on Webflow which supports webp. But, I have a large commerce site in sqsp 7.0. I sell photography. Webp is a pretty big deal if I can cut out 2/3 of the site's meat.  
I'm looking at a few files I did for comparison. The jpeg fed into jpegmini is 1.3MB. The webp at 65 compression is 500KB. I do a compare and there's not a noticeable difference in quality.
RE: Fluid Engine and 7.1 in general, It's clear that Squarespace's mission is: "Design anything without knowing how to design". Feels like it makes designers' lives harder but I need to probe further into FE. 

I've become quite concerned reading through this thread. The fact that sqsp has spent so much effort developing Fluid Engine (which seems to scramble the DOM) and has neglected WebP format makes me worry about their priorities.

Been following this thread for over 2 years now. STILL NO WEBP! - It's absolutely shocking to me. Wix's presence at BrightonSEO and their focus on SEO improvements is making it harder and harder to recommend Squarespace to clients. No .webP support is seriously hurting right now.  I'm not sure I can justify recommending SS anymore. Sad and annoying.

After scores of people had to rebuild their 7.0 sites to benefit from the new 7.1 features, SQ would do some real damage if they'd force their customers again this way.