As long as vehicle manufacturers are trying to sell their nav systems they are not going to enable pairing up portable systems to work in integrated manner like their own. Chrysler has a deal with Panasonic and Roadmate for their built in nav product. All you have to do is look at the price they get.
If we could buy a bluetooth GPS, pair it up, and have it interface like a cellphone with uconnect then who would buy their built in system ?? I doubt you can find any vehicle like that.