Well it kinda fragments the effort. Each campaign has to essentially do the same things, but twice.

endof10.org is hosted on KDE infrastructure, why are there two competing initiatives?

Don’t know of a solution that does this, but you could solve it with a two-step process. First, rsync the files to the server as-is, then use a background job on the server that converts lossless to lossy every hour or so.

Storage is really cheap these days though, why compress lossy in the first place?