Here is the ETOP 138 routing:
http://gc.kls2.com/cgi-bin/gc?PATH=g...YLE=&ETOPS=138
Financially, I actually think this route might work for DL. This would not be significantly different, from the perspective of distance or time, than going via Europe to South Africa. The fares to South Africa are relatively high, which means that the plane does not need to be full to make the flight profitable. And the demand for travel to South Africa keeps growing, justifiably.
My personal opinion, if Delta is thinking strategically (there is a first time for everything), is that this might be Delta's attempt to establish itself in that market using current equipment until such time as Delta can afford the 777-200LR, which could then operate nonstop ATL-JNB or ATL-CPT. South African made the decision to use Airbus equipment for the ATL-JNB route, and as a result now has that hideous operational stop at Sal Island both ways to/from South Africa. A nonstop service in both directions would be very attractive to the business traveler, and between Delta, Northwest, and Continental (members of SkyTeam all) this service should be able to generate enough traffic to reasonably fill the plane. Remember, the fares in this market are high enough, and the demand for business travel great enough, that you don't have to pack the plane to make money.
And given the very, very limited existence of award seats on SAA, it would certainly be nice to have an all-Delta option for award travel to South Africa.