policy-uri is slow

To confirm my understanding, if a document has a CSP policy consisting
of a policy-uri, then the user agent is supposed to block processing
of the document until it finishes fetching the policy-uri, right?
That seems very bad for performance.

In a similar vein, how should the UA behave if it encounters a
policy-uri in a CSP policy in a meta tag?  Should it block parsing the
rest of the document until it fetches the policy-uri?

Should we drop support for policy-uri?

Adam