Clearly Heathrow Hub believe that no matter how dead a horse is, it can always benefit from a bit more flogging.
Indeed. Apart from being untried and untested anywhere in the world, the Heathrow Hub proposal has one very important flaw: in order to increase capacity, permanent mixed mode is required with no respite for any flightpath residents at any time.
That would be unacceptable to everyone, especially supporters of expansion, including Heathrow Ltd..
Sometime in the future, once aircraft are even cleaner and quieter than now and mixed/segregated mode operations are no longer an issue, and once the technical and safety concerns are sorted, the Heathrow Hub proposal could be a template for a 4th parallel rwy.
However, it's academic for all of us, we'll all be long dead.