TL.
Obviuosly, under NAS, as both are VFR in enroute airspace, they won't be using the radio. Relative speeds, angles of attack, sun, haze etc have nothing to do with it. The primary, secondary and be-all-and-end-all method of missing is see and avoid.
The NASites will argue that in that scenario, would the aircraft have actually collided? The answer is: Probably not. Even if they miss by a foot, they didn't collide. But you roll the dice enough times, you get double 6, or in this case 666. This doesn't seem to bother them.
Some of the rest of us might like more than a bee's dick between us and a horrible, unnecessary death.
The very scenario you describe is what Dick & co. rave on about. Unnecessary use of the radio. In their opinion. Read Dick's posts. VFR aircraft shouldn't be talking on the radio. This is the philosophy driving NAS, and about to be visited upon all airspace users, like it or not. Do you get a feeling for where some of the opposition is coming from now?
eta23. ATC jobs my arse! Controllers won't be the ones doing the crashing. NFI, mate, NFI.