Thanks for the suggestion.
It looks like we already have an open feature request over on our GitHub.
It's something we are likely to look into later down the line, due to the small size of contributors (all who are doing so in their free time without any pay), this is a low priority request for us.
As FOSSBilling is still considered pre-release software, our primary focus for the time being is to resolve existing issues, streamline the codebase, and work to modernize things so that using, maintaining, and building FOSSBilling becomes a simpler process going forward. Once all of that hard work is done, we can begin to focus more energy towards implementing new features and functionality.