There are no SkyTeam carriers on which one can use DL miles to upgrade. It's forbidden by the rules of SkyTeam because DL does not offer IFC, so we cannot do a SkyTeam upgrade with miles into IFC. Nor can we use DL miles for award tickets in IFC by the same SkyTeam rule, although until a year or two ago, we could get IFC award tickets on SQ with DL miles. (sigh)

However, IIRC, in the past some have had luck with doing a SWU upgrade from an expensive business class fare code into IFC on AF.