The only thing that would actually make sense that McConnell is doing is possibly this.
1. Refuse to sign off on any nominee
2. Wait til trump gets nomination
3. Wait til it becomes obvious Trump will lose
4. Take up moderate nominee before Hillary becomes Pres.
So hold off now until things shape up. If Rubio wins he might think they have a chance so it's worth waiting. But if it's obvious they'll lose the election, he'll cut his losses. And by then it might be too late to be primaried as well.
No way does Obama give them a moderate nominee if they wait that long. He'd give them one now, but once it becomes clear Hillary would win that's the end of their leverage (especially if it also looks like the Senate will flip).