If it's your server and you want to have an easy access to your emails, then yes, but if you have a hosting business, then it's not a good idea because you're a 3rd party for the end user. In their own wordsI do not understand you in this point. Why could you not install it on your hosting server and use it as mail client? It is designed as a mail client when I read the site. Privacy is kept by the hosting provider. Python could be installed.
https://github.com/pagekite/Mailpile/wiki/Security-roadmapMailpile is not designed to be "Software as a Service", as given current technology, we believe SaaS to be incompatible with goals 2.2, 2.3, 2.4, 3.1 and 3.2, in addition to going against the high level goal of fostering user independence.
Python can easily be installed on many platforms, but CB and DA rely on PHP, Bash and perl. Adding Python would mean making sure it installs and updates properly on all platforms, including all the dependencies.