this is an absolute necessity!
I would like to see the ability to calculate:
- subtotal cost of each subtask
- subtotal cost of each task groups
- total cost of project
- subtotal cost of each resource
and it would be interesting to be able to calculate the same results for a range of time within the project as well. that way, we can look at a subsection of the project.
I don't know if microsoft project can do this or not, but if ganttproject can do this maybe others will follow!
and this new feature will likely change "under the hood" as new cost mgmt features get added too.