This request was deferred to a later date, because of the ramifications of removing no-transform that require careful consideration: If a user's permissions ever change for any reason, their access to pagespeed-cached assets would not change, which raises a security vulnerability.
It seems the best solution to this problem, when a pagespeed support option is enabled, would be to decrease the Expires header to 5 minutes and to remove the no-transform header, but to only apply these changes when the user viewing the asset is a guest. But this requires that pagespeed is aware whether the user is a guest, is able to use that information, and is able to pass that information to VaultWiki. It is not entirely clear to me yet from pagespeed's documentation how it handles user sessions and user cookies.