I agree that;
1) It’s a great concept
2) It’s certainly do-able by AP
3) It’s impractical to design and market a combination GPS-ads-b unit, for the simple reason that the market is too small. There is fierce competition out there for both technologies, and a $1000+ (?) combination unit wouldn’t sell in a high enough quantity to ever recoup the development costs.
But I do like the idea. Too bad the ads-b requirement wasn’t a higher priority about 4-5 years ago when I upgraded to the 740!