Would be extremely useful to have a configurable set of text attributes
associated with each object. The attribute values should be editable in
the object properties box.
Another helpful feature would be the possibility to run a system comand
from each object's menu, passing the object (type, name, ...) as
arguments
to the command.
Having both features will permit you to use Dia as a graphical workbench
to build CASE tools and the like.