Playing on Linux is not the issue. The issue is that EME + CDM introduces an 'Open Web' standard that cannot in fact be implemented by anyone who chooses.
Say the W3C decided to add a new tag to HTML, called '<happy>', that displays a smiling face. Anyone who wishes (Firefox, Mozilla, you, me) could implement that feature and start properly displaying content that contains <happy> tags.
This is not true of encrypted content that requires a proprietary, closed-source CDM and / or a secret key to operate.
That is why EME should be rejected by the W3C. Lack of Linux support is a consequence of the problem, not the problem itself.
My reading is that ESE is intended to work in much the same way -- the main work is done by the Content Decryption Module, which is more plugin-like. And indeed, the way existing DRM-using systems work in the browser is with the embed tag.
The spec says "The Content Decryption Module (CDM) is a generic term for a part of or add-on to the user agent that provides functionality for one or more Key Systems."
Say the W3C decided to add a new tag to HTML, called '<happy>', that displays a smiling face. Anyone who wishes (Firefox, Mozilla, you, me) could implement that feature and start properly displaying content that contains <happy> tags.
This is not true of encrypted content that requires a proprietary, closed-source CDM and / or a secret key to operate.
That is why EME should be rejected by the W3C. Lack of Linux support is a consequence of the problem, not the problem itself.