HEATHROW

[FlightPathOBN]

The basic decision on those distances was the studies showed that the most critical phase of flight for a wake vortex encounter was about 300 feet above threshold or a wingspan.... This is where the ac is in final config, near stall, and a Wake vortex encounter would have disastrous effect.
Wake encounters further out are not fun, but there is much better chance of recovery.

The wind profiler going up to 1000m gives a better idea of the conditions of winds aloft, looking specifically for wind shear levels and inversion or marine layers. These layers can cause a vortex to hang or even bounce. The winds aloft is real time, and this system, to me has quite a bit ov value, with winds at 5m, really defining winds for that runway end, and a very good definition of wind shear levels, and direction for config settings...

For the queue there are really 3 variables that set the separation distances, ROT, radar Sep, and wake sep.
The real time measurements show how long it takes for the flightpath to clear of the wake. This allows for other variables to be the controlling factor for the spacing, such as radar sep. So depending on the local conditions, you may be able to have a 320 follow a 744 at radar sep.
Balancing and blending the queue, not specifically for LHR, but others as well,
again, LTH with the 2 runways, bring the mediums in pretty fast on final, and the larger ac slower on a different runway, so the benefit of the system would be when you have the inversion and marine layers, or even a tailwind, that hang the vortex on final. This is an issue even when following a similar aircraft at radar sep, and the system will warn of this, as well as windshear, updrafts, downdraft, and microbursts.
(looking at LHR, with the mediums coming on final at average of 170kts, flaps are probably what around 20/25? This will generate a large core and a small core vortex on a 738, small core disapate very quickly, and large core tend to stay around longer, so the MET conditions with this approach speed and radar sep, would appear to be critical to look for a marine layer rising at night that would hang the vortex, of an inversion layer that would hang or bounce it as well...)

The transition times between reduced/increased operations can be much more finite, knowing exactly when the front has moved into or cleared the approach path, providing the data for informed decision making, and taking the guesswork out of the situation.

Yes, the spacing required to maintain the integrity of the ILS is not an issue with GBAS, so the spacing can be reduced. A runway end can be used for arrival and departure, but that's lemming talk in many ways...

I jumped the gun a bit there, I meant to say if you are using GPS, ie RNP transitions to a GBAS final, you break the 250HAT for RNP, and get the minima down to CAT III autoland. This transition is seemless.