I just thought I'd resurrect this thread because I now have a good reason to actually do something like this.
Did anyone take this any further?
Going back to something I missed in the original post by giantsfan3
the above level-translator IC based solution should work bi-directionally, for all signal types (digital I/O, PWM, analog lines, Serial, SPI, I2C),
Does the GTL2000 pass analog OK, it's only a few FETs so I would assume so but haven't tried it.
Rob