As an extra LHR "opinion" on the heli ops into Egham.
Whilst you as the pilot of the heli might be able to see the inbound and outbound traffic, (and perhaps you can assume the pilots of said inbound and outbound traffic can see you) for ATC to provide separation between your hell into Egham and the Heathrow IFR traffic there needs to be a set of criteria applied.
One of these is maintaining visual contact with traffic. Not always easy to see a helicopter in the Egham area despite what the weather reports say and how the weather looks in the immdiate vicinty of the Egham area.
Class D "might" assist in this, but until the procedures are decided it would be remiss to assume they will enable freedom for hell ops around Heathrow.