I was told by a member of management on a flight a while back that CPT and JNB bring BA some of the highest yields on the network. The CPT route got an increase in capacity following SAA's withdrawal, and may get further capacity again during the summer season (Oct-Mar). CPT is a significant leisure route which is not so affected by 'seasons' as it is fed year round by significant demand from both the US & Canada and Europe. While % load factors on CPT are higher in WT and WT+ than they are in Club World (although F load factor is very healthy), the route is very demand inelastic and demand is not significantly affected by price increases. This is in part because there is a substantial market for a direct flight between the UK and CPT with the increasing number of middle class South African families who travel from the UK out there year round (as well as it being a premium holiday destination for Brits), and they don't want to fly via the middle east, which adds typically 8 hours to the journey time on a typical London-Dubai-Cape Town itinerary.

BA's prices over the past 5 years on the CPT route have seen some of the fastest increases on the network and they have been able to sustain them. Cue further price hikes during Oct-Mar periods, which is when VS were competing. Whether or not BA decide to feed the route with further capacity increases during that season will probably be dependent on other factors not related to CPT (slot restrictions at LHR and aircraft availability etc).