Having never flown the Manchester LLR, I base my comments on the rat run between Stanstead and Luton - an area I know well and one that gets reasonably crowded with aircraft and microlites.
In principal, I think the idea of unmanned frequencies at GA pinch points is a great idea however lets bear in mind is that not all things that we roam the skies in are radio equiped and that the law created by Mr Murphy dictates that someone, sometime will rely on everyone being able to announce their presence and will fail to lookout to the commensurate degree and at best a near miss will occur, and at worse, people will get killed.
Maybe if we were to go to this kind of frequency, we need also to make it the law that all flying machines are radio equiped (and the radio is turned on!! ). These days, the equipment is relatively cheap and the advantages far outweight the disadvantages. I notice from the LAX example, there is the need to tune to a frequency and therefor non radio traffic would presumably be barred (a sub question - are non radio aircraft allowed in ther US ? ).