If T6 is built west of the MSCP of T5, and then they both become Heathrow West, so it is not an extension?
OK, have it your way.
T6 was originally North of the airport with the 3rd runway.
Yes, the original 2009 proposal for a shorter northern R3 of 2200m showed a T6 sitting slap on top of the M4 spur.
The A304 will be moved for the comfort of this "extension" as it is on the plan, together with the disappearance of the A4 Bath Road. None of the consultants at the local briefing could explain about the movement of these roads.
The latest plan I've seen does indeed appear to suggest the A4 Colnbrook Bypass being interrupted by R3 and T6B and the A4 re-routed along the original Bath Road route (through Colnbrook and Poyle) to a roundabout just west of the M25 (by the golf range), then tunnelling under the airport to resurface and join the original A4 at the Hatch Lane junction.
It's not altogether surprising that they are being coy about publicising that.
Re the A3044/Stanwell Moor Road, that's replaced by a link road west of the M25 from the aforesaid roundabout to the J14 roundabout, then via Airport Way to rejoin its original route.
Neither could they explain fully the ability of all aircraft to "touch down further along the runways to reduce noise"
That features in a number of Heathrow's recent presentation documents, which talk about displaced thresholds of around 700m on the current runways. That would result in aircraft being about 120ft higher at any point on the approach, which would have a fairly minimal effect on noise.