I have used Agile Methodologies in an IBM i RPG and ILE environment. It
was as successful as any other language can be if managed properly and
supported. It helped that the developers were open to new technologies and
modernizing code had been a priority IN RPG for the organization for many
years prior to the adoption of Agile techniques.
One thing I have learned between working in QA in Agile and Waterfall
environments is there is no single answer. And there never has been. RPG
doesn't face any more complications in Agile then it does in Waterfall and
if it is the right language for the application it can be implemented.
There is much more to my opinion than this but it is the best answer to
your first comment.