Oh that's undoubtedly a lot, of course. If Plex somehow prevented (built-in CV detection of anything commercial vs. home video being played from your own library, say) pirated content I think MAU would drop approximately 100% though!
Ripping a DVD collection to which I own the originals is not piracy in my country.
In fact, we pay a tax by the GB for every writable storage medium we purchase (everything, from HDDs to the SD card I load into my camera, including actual phones) that goes to authors and accounts for “private copies” like those.
I use Plex and the RAWs from my camera take a lot more of my media server's HDD than any DVD rips.
I sympathise and think that should be legal in any country (I've long thought that the sale should be of 'the right to view' more than the physical medium, Sony and others toyed with it for BluRay which I was thrilled aboutthe potential future of, but canned it recently-ish) but I don't think that materially affects my hypothetical, for one thing it could trivially be applied only to other regions.