I understand the case for interoperability between different media sources, but what looks like a glaring omission is that nowhere on this page does it mention whether it is a pro-DRM concept or not. If it does support artificial restrictions it doesn't solve the problem of "not actually owning your content" (their words), which is a problem created by DRM.
Clearer wording on their site would be welcome.
What I've seen in the wild is companies implementing OPDS up until the part that involved actually downloading and decrypting of content, at which point their in-house system takes over.
There are lots of folks running OPDS servers for personal use. The few most common ones are ubooquity, elibsrv, calibre, and cops.
Lots of eBook readers also support OPDS now- I use koreader on my Kindle, and Moon Reader on my Android.
I’d love to lurk around but these dropdowns don’t work in Safari on an iPhone :(