VS may be actually be a member of Skyteam by then (there's some speculation out there about a late January join date). In which case, DL STE+ status on a Skyteam flight should in theory provide access to VS Clubhouse at JNB. Even if they adopt DL's more restrictive lounge access rules (which wouldn't surprise me), I would suspect DL STE+ in PS cabin would likely provide access (as it does to Sky Clubs).