Maybe it's just me, but it doesn't look clear why do we have JSXNamespacedName in spec, if, as far as I remember, after long discussions JSXMemberExpression was introduced exactly as replacement for first one (it's not supported by E4X but looks more familiar as for JS).

Or was it just for React (which emits error on trying to use namespaced name) and :-based namespaces were preserved for DOM-based JSX implementations?

It's somewhat confusing, so if there's reason for both to exist, maybe it makes sense to add a description cases in which one or another namespace syntax should be used. If there's no such reason, then maybe it makes sense to remove it from spec as deprecated so new tools wouldn't have to handle it.