I’ll skip the humor, as Tonda took care of that. This is NOT a good idea.
This proposal is meant to address the situation when a user without the plugin accesses the site. Of course the proposal also handles users with the plugin (by not doing anything for them).
The Tor Project hasn’t found a better solution than to simply ask people to download the browser from their Web site or some other trusted place (if you can obtain the checksum from a trusted source). Some degree of trust is necessary, but I’m sure they thought of and declined to use redirects.
Months ago I discovered (and posted here) that Amazon has a pending application for the TLD .safe. Now I learned that Tor managed to solve “the Namecoin problem” by reserving .onion. It took them 10 or so years to get there so even if the next project secures a similar compromise faster, it’d take years. But it’s a good breakthrough for them and all other projects that may want to take the same route.