That would sure suck if it happened.
Yes, it would, but in a certain sense I don't know that it helps that we're talking about Duke.
That would be 2 years in a row that Duke pulled some academically sketchy last-minute maneuver to snag an elite player. Vernon Carey might have a perfect SAT score and end up a Rhodes Scholar- I have no idea what kind of student he is- but has he been planning to graduate in 3 years since he first started HS? Something like that usually involves a lot of planning (unless you're Marvin Bagley).
There are other schools in the NCAA besides Duke. There are other schools in Duke's conference. I think there will be a lot of turned heads if it starts to look like Duke can get any player eligible at any time that suits their agenda, in ways that don't seem to be an option for everyone else.
But I can't be totally hypocritical about it, since I'm rooting for UK to pull it off. If someone, UK or Duke, gets a kid at that level to commit to playing 2 years when they don't have to, it's a huge coup. And I guess you can kind of, sort of, look at it as something like all the football recruits who enroll in college early (though that's just by 1 semester, not a full year where they're actually playing for the team).