He would be in the right and plenty of people would care. The Supreme Court is serious business and a big fight over leaving a vacancy open for over a year would draw some attention.
I agree that the vacancy would draw attention but the GOP could just as easily frame it as Obama being partisan and trying to force an activist majority on the court. It's in Obama's best interest to try and cut a deal with McConnell.
Conservatives would be the only ones to buy that activist talk. Obama doesn't need to cut a deal, because he is within his authority to select a nominee for the court. It's Republicans who have something to lose, not Obama.
And the Senate has the right to disapprove it. The founders never intended to give the president quasi-absolute power here.
But look at the statements from Mitch McConnel and the rest, they aren't taking issue with any particular nominee. They aren't waiting for Obama to nominate someone and then manufacturing a pretext to oppose them. They're dropping all pretenses and going straight to saying that it's sonehow fundamentally wrong for the President to nominate anyone. That is indefensible.