Yeah, implementation of this could be handled by a Redirect, however in my system I didn't allow users to redirect any domains/subdomains externally (at least through the vhost) so I don't even need that feature. That is a nice feature request though, and I'm sure my clients will find some use for it.
I really think I just need a feature to set the whole domain as a "Clone" of another domain on the server. Browsing them could either keep you on the same url (redirect/forward), or allow them to have different urls (ServerAlias), depending on the option chosen when setting it up. Either way though, the cloned domain/subdomain woudln't need a DocumentRoot so that bug #896 does make complete sense.
In my implementation all of this is done simply with ServerAlias directives, but yeah I agree using Redirect gives some more flexibility. (not sure of the extra overhead it has though, if any...)