In message , at
11:59:03 on Mon, 26 Nov 2018, NY remarked:
Yes. Various rail links to the west and southwest have been under
discussion for decades, and still are. The station under T5 awaits
the line
west, but construction still hasn't begun.

Crossrail will help a little, but it's not enough.

I'm not sure why a north-to-west facing curve was never built between
the Heathrow spur and the GWML, to allow trains from Reading, Oxford,
Bristol and south Wales to reach Heathrow - even if it involved a
change to a Reading-Heathrow shuttle.

There were proposals at one time to build a spur from the
Reading-Ascot-Waterloo line near Feltham to serve Heathrow from that
direction, but I don't know whether that is still on the cards.

Both such routes were hailed in BAA's annual report 1998, as well as HEx
to St Pancras in addition to PAD.

Is it any wonder I'm a bit of a caller-out of rail industry vapourware?
--
Roland Perry