The area concerned (Echo apron)was built to provide more remote parking for mainly B737-800 size types. The whole area wasn't paved because the business didn't demand it. Should a second runway ever be built then any new taxiways would easily link into this new apron.
Also it's located so if another satellite was to be built it would fit nicely between the two cul-de-sacs (Delta and Echo). As for terminal access to this new satellite if it was a walkway then the very long distance would be a customer service issue. If the transit was extended this would be a very costly project.
Given the present traffic downturn I think it'll be a long time before a new staellite is built. Maybe when Stansted is sold the new operator may look at things differently.