The limitting factor on the 77W and 77L into JNB is the tires. At V1, which is higher than other other airports due to the altitude, the aircraft would be traveling at such at such a speed that they would catch fire. It's an issue Boeing is working on with BF Goodrich, and is the same reason Delta will not be flying its 77L's into JNB for the foreseeable future.

As for routes, I doubt these planes will be put on ME or East Coast NA, as it would be a waste of capability. LAX, SFO, BKK, HKG, and Maybe CPT are likely destinations IMO.