By this sentence, you made me think if both could be put on a single display...
As they are using different physical effects, they may not interfere.
Not sure which one would have to be on top (probably the capacitive, otherwise the resistive grid might shield it from the finger ?).

Searching on the net, I find mainly things about a patent by RIM in 2009 :
https://techcrunch.com/2009/08/05/ri...e-touchscreen/

and also this:
http://www.intomobile.com/2009/12/30...oming-in-2010/
(but the company closed in 2010 : http://www.touchco.com/)

Not sure anything as seen the light right now, but it would be interesting if anybody has info about this.