Indeed, this could be a stand-alone SW.
It could be delivered by Plex or by another party.
It just makes sense for Plex to dig into this imho and run this as a community effort.
Sense = 
… since Plex is a business after all (no offense).
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Viability. Plex have in-house resources and a supportive community. Plex can mobilize the existing user base to crack the chicken-egg-problem of getting fingerprints into the database to make this work. Being in the lead helps Plex to steer the efforts so that Plex benefits the most.
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Maintain and grow user base =
. What sets Plex apart from “the Netflix way” (and I like Netflix) is that Plex lets me integrate my own video content. But data management is a major barrier for entry to the Plex world and an ongoing cost. Reducing this cost and barrier will nurture the user base. -
License =
. Even with OSS software and community efforts, there is money to be made. The suggested solution plays in a different league compared to everything else. I imagine a world where the default advice in user forums would be “Buy Plex Match and be happy”.
This is the way. 
