The phylogenetic tree of this loop is indeed interesting (ACE2 binding motif). We have been working on this too. Using the same data set as we used above with six new pangolin sequences, we find that the clustering with ACE2 using bat strains (labelled red, experimentally verified see Functional assessment of cell entry and receptor usage for lineage B β- coronaviruses, including 2019-nCoV) suggests the ability to use human ACE2 may have been pre-adapted before jumping to humans in a bat species or there may be other regions close to RBD involved to determine ACE2 usage.
The pangolin strain, which causes clinical symptoms in pangolin, may come from a bat species originally. We may still need to find the actual intermediate animal.