Hi,
transparent proxying to TOR Hidden Services is a great feature of the TOR daemon when it comes to other applications/protocols than HTTP and surfing. It would also be great with privacy appliances (e.g. Mailpile using TOR as secure SMTP transport channel).
John Does have problems with such a setup because of the NAT firewall rules.
So I suggest the TOR daemon should automagically set the necessary NAT-rules on Windows, Linux and BSD when "TransPort" and "VirtualAddrNetworkIPv[4|6]" are configured in torrc.