Yeah good point, that actually brings a lot of complexity in our player library.
There is already bugs linked to specific DRM systems, but it only becomes worse when we talk about specific devices, like STBs or connected TVs. Some who have completely different systems than those three, some who lie on more robust implementation of those three. I ran into multiple kind of bugs, sometimes CDM-related, sometimes browser-related (CEF), sometimes a subtly different EME workflow was needed on the JS-side (we could argue that in that case the bug would also be more on the browser/CDM side if it does not just follow the EME specification).
I hesitated to talk about EME-related matters in that article but here (on an introduction) it would have become too technical and less interesting for most common folks.
But it would definitely be a good subject to talk about for another article.