Since this is still work in progress, this comment was mainly adressed to PR reviewers and testers.
Definitive information about this new parameter should be added to the NEWS.txt imho (we just add a parameter to a function, this is documented in last versions of this code, and if not enough feel free to propose improvements). 
This plugin isn't intended to run on old picard versions according to Sophist (i dunno if it is acceptable to run it with "normal" priority).