Potential customer wants to upgrade an application because they feel it is too hard to add features. The app is 10+ years old and uses unsupported libraries. A majority of the customer's customers use an even older Perl application but they are trying to move people from the Perl application to this "newer" application.
The first question to their desire to upgrade should be "Why" as in "Why even keep this application". You are better off spending time reaching out to customers that use the Perl application, find out what they like and dislike, and just implement an entirely new application and get rid of both previous applications.
Potential customer wants to upgrade an application because they feel it is too hard to add features. The app is 10+ years old and uses unsupported libraries. A majority of the customer's customers use an even older Perl application but they are trying to move people from the Perl application to this "newer" application.
The first question to their desire to upgrade should be "Why" as in "Why even keep this application". You are better off spending time reaching out to customers that use the Perl application, find out what they like and dislike, and just implement an entirely new application and get rid of both previous applications.
Most likely they will cost the same.