Probably T-2020, since that's about the time frame it will operate in and it offers a clear vision of the future for advanced pilots. I wish I was kidding, but the old designation system is about dead. It's now about marketing; T-6 (A reference to the original WW2 NA Texan), the B-21 (not B-3, because it's a bomber for the 21st century), and whatever other programs they've played with the naming convention for better marketing.