In uk.railway Recliner wrote:
Stansted is running at well below its runway capacity. If it ever grows to
need more passenger terminal capacity, it will simply need a new, fourth
satellite replacing the current cargo terminal, with a station on the
transit line running directly underneath. There's plenty of room to move
the cargo handling area to the west, or north of the runway.

There's a plan to build a new arrivals terminal, to the northeast of the
current terminal building:
http://www.bbc.co.uk/news/uk-england-essex-39507329

That will presumably mean some rejigging of pier walkways, or else another
stop on the transit (it's roughly where the depot is now).

It will presumably also block any attempts to extend the Stansted railway
branch eastwards.

Theo