Can you explain how such a tree would map inside a graph? I can't think of an obvious use case.

The use case is something like this: http://ludo.cubicphuse.nl/jquery-treetable/

It would be nice if something like that existed, but with much richer features like the libraries above.

IIRC, both datatables [1] and JQGrid [2] do this, right?

[1] http://datatables.net/

[2]http://trirand.com/blog/jqgrid/jqgrid.html

How about editing csv files in a git repo?

how much money is that worth to you?