At that point, you might as well have your own web server side connect to Tor and do what you want, it's not hard w/ libs out there. Otherwise, if I see this on your site, I just might start using your proxy as my new tor2web, heh (not that there is real value over just my own Tor client running locally).
Note that it's not a replacement for the Tor browser: it is not build for the same usages. A good example is people implementing privacy-oriented tools with strong cryptography in Javascript to drives adoption. The goal is to improve the privacy of such partially honest services by bringing anonymity into the picture, with a better compromise than a "trust us to not log" policy.
You can even fantom models where a commercial service provider focused on privacy push its users to use the Tor Browser while shipping a Tor client by default to its user that didn't bothered installing one. Because at the end, it will be easier to keep your promises about not doing logs if you intentionally forced all of your users through the Tor network.
If the "walking onions" proposal gets maintstream (i.e. private retrieval of a consensus subset), we can hope for improvements (see https://gitweb.torproject.org/torspec.git/tree/proposals/300...).