1. Dual channel ADSB-In (uat and 1090)
I'd second that. I think over time the 978 UAT is going to be less and less a common offering from vendors. I think the FAA created a system that's neither flesh, fowl nor good red herring by trying to split "GA" users from the "bigger" planes above FL180. Should have just done like everybody else and use the same 1090 for all.
1090 has some advantages over UAT that will, I think, grow with time...
UAT gives us the weather info and such, but as far as Out goes, I think the majority is using 1090 based on actual users so far.
The FAA does this kind of thing regularly--they say "here's what we
think everyone's going to do, so let's write the rules for that"--and then in the real world everyone does something else. Look at light sport--the FAA genuinely, truly, 100% honest-to-goodness, Scouts' Honor thought that the vast majority of LSA's would look like "fat" Part 103 ultralights, top out under 87kt, and be used primarily for training ultralight pilots*. They apparently are completely ignorant of human nature and it never occurred to them that the majority of designs were going to cluster right at every limit they set, that they'd be flown most often to get around the asinine medical requirements, and that every trick in the book would be used to push the boundaries while barely keeping within the letter of the law.
I think what's killing UAT for Out is the requirement to keep a "standard" Mode C transponder as well. That's more equipment and weight, and if you're spending for ADS-B you might as well take the box out if you can. International compatibility (or more precisely, the lack thereof) may be a factor, too.
Personally I don't see why you'd develop a system that did Out on one and In on the other, and rely on FAA rebroadcasting to get the rest of the traffic. Dual In capability should have been the baseline.
* See FAA's comments on the final Light Sport rule in the Federal Register...
