I spoke with someone at the last Edison NJ Greensburg show. He was running a mth cnj gp 9 using Airwire. I looked it up after the show and found the cost per loco for conversion far too high for me. I'll stick with my fleet of TMCC and ERR conversions since I already gave the layout built and wired.
Until you can afford to convert all the locos you want to keep, one option would be to put the decoder in a boxcar or trailing car. Then all you would have to do is add a discreet tether to each loco you want to run, along with a DPDT switch. (This approach also solves the issue of how to get the signal into a metal tender shell. ) When you're not using the Airwire R/C, you could tuck the tether back inside the body.
I've seen both of the major proprietary systems struggle on large layouts, and with certain track arrangements (i.e., closely spaced yard tracks, over & under, wire mesh tunnels, etc.) I happen to like the Airwire controller, and R/C direct to the loco has a lot of advantages.