Given Emirates' success from LGW it doesn't seem unreasonable that Qatar might also make a go of it, perhaps using a B787?
As for TCX to Cape Town, that sounds like a great route addition. With not great competition on the route, they could do really well. Good luck to them.
I too agree that there's a case for both LGW and LHR to get new runways. It probably will but doesn't have to be an either or.