May be some benefits from combining a couple of performance ideas:
1) T27611 -- support creating WebP thumbnails to supplement jpeg & png
2) T110615 -- dynamically loading thumbnails via JS to reduce network competition during text load
A big holdup on WebP has been getting them served in a backwards-compatible way without preloading the jpeg/png. If the image load is getting triggered from JS anyway, it should be trivial to toss in a ".webp" at the end of all the URLs.