Been thinking for a while about a JavaScript-free way of automagically redirecting #Tor users to the Hidden Service (HS) address (assuming a site has both).
So far I see two options (and one work-around):
1. use a 300 Multiple Choices HTTP code with the HS and the regular addr. That would have to rely on Tor Browser choosing .onion over regular addresses by default.
2. Main site could have two iframes, one loaded from the HS, one from the regular addr, and two similarly CSS files.