So I just checked the 650m was released in march this year I do not know the exact date so lets say 10th, so thats about 3 months until apple released the macbook pro. If the gtx680m is being released early july then we can expect a release early october.
The current line of macbook pros have a new retina configuration so apple probably decided to wait a bit longer until the retina was "ready for consumers" (tested several times ,etc) and released them all together. Also WWDC was just up the road so they might as well have waited for the conference to announce the release.
I can guess like many of you, a retina imac wont see light this year and placing components on a AIO computer is easier than putting them on a laptop and retina/airlike laptop.
So I think mid july is plausible but late July-mid August is more likely. Anyways we are mid June already, so thats just a month ahead. If nothing happens then, well.. I am out of ideas.