Native RNDIS USB tethering support for OSX
Since then, this driver has come out. It's FOSS too.
http://www.joshuawise.com/horndis
RNDIS is a Microsoft-proprietary protocol and it's highly unlikely that Apple is going to support it just for the sake of Android tethering.
http://en.m.wikipedia.org/wiki/RNDIS
Your best chance is for a 3rd party to write a Mac OS X driver for RNDIS. Don't expect this to be free (as in beer) though.
However you should be able to use the Android phone as a USB dial-up modem, which was the standard way for tethering before the iPhone came about and still a supported method in OS X and others.
horndis is a brilliant solution - just started using it yesterday and it's completely stable
I couldn't get my Andriod phone to work as a USB modem.
I compiled it from source for 10.6.8 then used packagemaker
and the included packagemaker
project file to create a package to install.
Only gotcha was using sudo su
to change the ownership and permissions on the installed kext manually
sudo su
chown -R root:wheel /System/Library/Extensions/HoRNDIS.kext
chmod -R 755 /System/Library/Extensions/HoRNDIS.kext