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.