almost 2 years have gone by and still no clear statement.
Looks they are not prepared to share it with the open source community.
Luckily this not common practice
Hello everybody. I doubt somebody is still using mantis and use it as an agile tool but I give a try here
I enhanced lecturio's BurnDown plugin for Mantis and came up with a plugin on which you can estimate each task and follow your sprint's progress: https://github.com/lgrignon/Mantis-BurnDownChart
It is not mature but it's open source so anyone can contribute and enhance