Paul, (and any other interested people)
We are almost to the point of looking for a different hack, and this
one is much more difficult, but would open up many more options. It is
also beyond my ability, but I know the day is coming....
The day the printer firmware is hacked!
This may be the last method available to us to use our third party
devices and inks. This is a difficult thing to do because Epson makes
the MCU in their printers, and as far as I know they do not sell it to
anyone else. So data sheets and code is not available.
But your idea is feasable if that's really how the final ink sensor
works, it could be something else and not resistive at all, could be
capacitive, or less likely inductive. The idea of using something
similar to the large format dampers would be the same thing that Ink
Republic did, so that design is already there.