Thanks for submitting this. The particular change that CSSPseudoElement no longer inherits from EventTarget, instead participating in event handling as Event.pseudoTarget which is a CSSPseudoElement improves compatibility and therefore sounds reasonable on its own. The CSS Working Group's resolution to “use the CSSPseudoElements interface for all standardized tree-abiding pseudo elements” also seems like a reasonable general extension to CSSOM.

Our concerns are regarding the accessibility implications of making pseudo-elements interactable, especially when applied to those well established ones like ::marker.

While Event.pseudoTarget is a necessary building block, this on its own leads to design patterns that are not accessible by default. For example, in the event-driven interaction use cases, the pseudo-elements can react to mouse by listening to the click event, but not to keyboard. Making them keyboard focusable will be another major problem that must be solved

However, making existing pseudo-elements like ::marker keyboard focusable might break web compatibility. Existing AT might not be able to detect that a ::marker is interactable.

We agree that interactable pseudo-elements can lead to useful design patterns, but it requires a lot more work than this interface and have some concerns that that work should be done early enough.