Generally PBTNL's are of two types:
1) A marginal major leaguer, or major league ready prospect, who requires protection on the 40 man roster. However, the acquiring team does not have the roster space. So the name is withheld until space is cleared - maybe through another deal that is in the works. IF (big if) that's the case here, it could be somebody like Szapucki or Kilome.
2) More likely, the teams agree on a list of three or four younger prospects, and the acquiring team gets to choose from that list at the end of the minor league season. So if that's the case, we may not know for quite a while.