A really interesting feature for me would be support for “logframes”. They are a rather simple way of showing your project planning in a table style, but with integration into budgeting and gantt planning etc. they could become quite useful.
They are also more or less a standard feature in all NGO projects and were originally developed by the World Bank for planning their programs.
But there is basically no advanced tool that supports them, and everyone continues to work with Excel tables. But with the frappe/ERPnext basis it would probably be easy to create such an tool integrated with the other features.
Here is a short explanation how they work:
After much searching I came across three projects, one is a nice single user desktop software only (www.logframer.eu), the other one lacks integration and seems to have stalled in development (http://kashana.org/ runs on Django: https://github.com/aptivate/kashana) and the last is part of a huge Java webapplication that is developed very slowly and lacks most of the interesting ERP features (http://www.sigmah.org/).
So all in all, it would probably be an interesting feature for ERPnext to add, as it would be quite unique in supporting it.
If there is some significant interest in it (and maybe a proof of concept app), I could probably try to come up with some (limited) funding to support further development, but for now it is more of an idea.