We get the concept.
But a freq change in IF, where pilots are not departing flying published procedures, but instead doing pretty much anything you can think of, at a certain altitude is eschewing responsibility for your airspace (unless you only use the top of your airspace, which doesn't seem to be your goal, but instead to expedite the point at which you can start ignoring them).
If you're at EGLL and you tell someone on 27L to contact at 1000, then he turns due north into the path of someone on 27R, what are you going to do? They're gone. Extend upwind is no more.
This seems more useful for tower controllers who think the plane ceases to be their problem the second there's a breeze between gear and runway.