A problem with this particular approach is that chrome-trusted for example will no longer have access to the session's DBus, so it cannot show any notifications for example. And DBus, like X11, does not provide any separation right now as far as I'm aware (it has support for authentication, but in practice, `external` is used most of the time which is based on UID).
The only variant that might provide a real security benefit here is the -paranoid one, as that those not share the X11 server session.