The folks at WP Media team are currently adding support for WebP. The media library is more than just upload a file and put the name in the database. It is also
- all the JS for navigating around the media admin pages (edit, crop, delete)
- generate smaller sizes
- the JS to interface with the editor to handle images (insert to post, galleries, upload)
- gallery shortcode
- compute which smaller size to use
- generate
srcsetandsizesattributes
As you can see, some of these things make sense for JPG and not for SVG. The people working on WebP are trying to come up with a way to convert from JGP to WebP in a non-intrusive way, for fallbacks and caching and resource usage.