executive wrote:

"Piwigo will generate WebP files for multiple-size display"
Presumably this means webp derivatives will automatically be generated from webp source files.

That's right.

executive wrote:

But what about jpeg source files? It is sort of implied that they will be "replaced", but it's unclear.

We didn't imply that, at all. An original JPG file will have JPG files as multiple-size files.

I think it's a bit early for a full replacement and force everybody to switch to WebP for display.

executive wrote:

And in the future, will we have the option to generate webp OR jpeg, for ANY supported source file (eg HEIC)

Probably yes. The output for multiple-size could be an advanced configuration setting.