It's an interesting question about who will benifit and who will be hurt by the change. I don't think we know fully until we see it in action.
But I do think it helps deep 3pt shooters like Wilmore and Allbriton who can hit from NBA land if left open. It probably hurts the 19.9 three point shooters (the ones that aren't that great but can make a couple) like avier, King, Wilmore and even Noel.
As a team GW shoots less 3pters than most (12th in the A-10 in 3ps/game), so that's a plus if we assume they are now harder to make. With a switching/rotating D, 3pt shooters will still be left open and it may be somewhat harder to close out on them, but it's still a plus for GW on defense. The opposing players could have set up at 20.9 ft last year if they wanted but didn't because it's harder to make from further out.
I say net plus for GW. Net minus for heavy 3pt set shot teams like Davison, Vandy and Charlotte. Then again, it's only 1 foot so the NCAA basketball world won't be that different.