To my knowledge the Silhouette Coefficient isn't calculated as part of any SAS procedure or SAS Viya action. When I wrote the SAS Global Forum paper my goal was to discuss a lot of the methods that people use to evaluate clustering, but not necessarily limit myself to methods that are supported within the software.
There are some definite down-sides to the Silhouette Coefficient in that 1) you shouldn't use it to compare two different types of clustering - it's very much related to centroid based clustering methods 2) it is a time consuming metric to calculate if you have large numbers of observations.
That being said, I think that one of the better ways to implement if you are looking to do so in SAS would be by using SAS IML. Because the Silhouette Coefficient looks across all pairs of observations the matrix setup of IML would be an easier programming approach for this type of problem (as compared to Data Step - which is still doable).
