5D. South likely has nothing in spades, has to have "all" the points in the other 3 suits for his opening. I think with 16 HCP, LHO passed, partner opened 2nd seat, we almost guarantee 9+ diamond fit, and ~29 HCP. I will suppress my spade "shortage" as irrelevant for slam and 11 trick game purposes. I think, 5D it is. If partner is "extremely short" in spades, partner may still bid slam.