In my electric, I want to replace the neck humbucker with something to get as acoustic a sound as possible. Does such a product exist, or would the only option be to get a bridge based piezo?
you could always get an Acoustic Simulator like the one here http://www.musiciansfriend.com/product/Boss-AC3-Acoustic-Simulator?sku=151043
I think Piezo all the way.
this might not be accurate, but apparently Slash uses a Fishman Power Bridge, which is supposed to emulate an acoustic sound.