Definitely, but I suspect it already is one -- in which case you could vote for it.
The problem is that there's are no user-group-specific permissions at this point.
It might be possible to do something with a plugin attached to OnUserFormPrerender, but it would be tricky, and all users would still appear in the grid.
The user getlist.php code does accept a property specifying the user group to show, but even if you could set that, I think the user could just remove the filter in the grid and see all the users again.
A built-in solution may not appear until MODX3.
------------------------------------------------------------------------------------------
PLEASE, PLEASE specify the version of MODX you are using.
MODX info for everyone:
http://bobsguides.com/modx.html