It's not that much effort at all. I've heard of a group of friends who share a single D&DI account.
That's already anticipated in the business model. Gaming tables have been sharing the same set of print books among themselves since the 70s. People have been making photo-copies for a long time too.
Unlimited push-button redistribution of copied files across the Internet is the scale you want to focus on inhibiting.
But let's say that system is in place, and let's say it somehow prevents people from sharing IDs and passwords (and the actual files).
It doesn't really need to do so. Sharing (as opposed to creating copies and distributing them) requires an element of trust. Just like someone can run off with your real books someone you give the ID and Password to can jack your account. That means you don't hand your stuff over to any random chumley on the 'Net with his hand out.
The pirates will extract each book (or just scan the physical copies), convert them to PDF, and upload them to torrent sites.
That's why you need a good lock-and-key software system and to rotate your encryption regularly. Yes, eventually someone breaks it and rips the PDF. If it takes a prolonged amount of time to do it then you drive the people who want immediate gratification towards legitimate channels on release. The same logic applies to how simul-casting streaming releases cuts into the demand for fan-sub anime and why late-coming video game cracks don't bite much into AAA title releases.
If you're a legitimate customer, you have to go to the WotC site, faff about with product IDs and such, give them money, and end up with a restrictive, proprietary, massively inconvenient product.
Restrictive and proprietary are non-issues as long as inconvenience is mitigated by good design - hence the platform agnostic angle. If you all you need to do is install a reliable application once and then it works, well that's not really a stretch from needing to download Acrobat Reader.
Beyond that if you want to buy a PDF from you've got to faff around on their web site to make a purchase, so that's pretty much a non-issue.
That's a start. It gives the customer a service he actually wants to use, rather than just devaluing the product.
Between having current errata and forcing significant lag time between legitimate product release and illegally cracked software release you'd could make the impact you wanted to. The other nice feature is that as Errata releases come out the app knows the right one to fetch immediately - no waiting for a crack and then wading through torrents clogged up with obsolete versions, low-quality versions, corrupted files, and malware.
- Marty Lund