In the video where he announces the challenge (not the livestreams where it’s initially brought up) at around 2:45-2:50 ish he specifies if the goals aren’t met we won’t get his tasteful nudes. Also in the second video about it at around 1:08-1:10 ish he says that when the new condition is met we will be provided with the promised tasteful nudes.
Although tasteful nudity technically doesn’t mean no nudity, just that the artful aspect is stronger than the sexual aspect, it is often done without showing genitalia. Just like in Mark’s tasteful nudes calendar. Although he might show more than that, it’s safe to assume that since he’s done tasteful nudes before, that they will be similar to those.