I think he'd just feel like a bit of a tit if they gave him a title now. He wouldn't want to use it while playing, as it would be distracting, so a bit pointless.
He's already been awarded an OBE for what he did up to and including last year, although he's not yet collected it. If they want to give him another award to acknowledge winning Wimbledon, a CBE is the next step up, and I don't think it would be controversial.
Knighthoods to active athletes always feels a bit silly. They've done it with a couple of cyclists (Hoy and Wiggins), but they were in their 30s. I'd say quite a few people think they were given prematurely. That said, most people would say that if Hoy and Wiggins can get them, not to mention Dame Kelly Holmes, then it's a lock-in for Murray to get one too. But just because it's inevitable, doesn't mean they need to rush it.