Oh, I think with the ~100 developers they have brought on board, this is exactly what they will be working towards doing. One way to throw a wrench in Beyond 20 would be to start rendering the DDB webpages as images instead of text. There are other more aggressive things they can do as well.
As someone else said, that would mess with screen readers.
It would also make the site unusable on mobile devices (tablets and phones) that rely on other resolutions. And you couldn't zoom in or out to change the font size.
And it would be harder to update as you'd need to make and upload a new image each time you wanted to fix a typo.
And having it based on images and not text would make the content harder to search, and less likely to show up on Google searches, unless the coders spent a ridiculous amount of time adding alternative text keywords.
I'm sure there are other ways, but as long as the extension can read the text and is being run on the user's browser not a lot is visible on the dndbeyond side. The best thing they could do is just launch their own extension that connects to the Foundry and Roll20...