First, an example of what I mean:
Basically, there would be a right-click menu option "Generate Instances..." that could be selected which would bring up a check-list of variables which used an "in list" initialization, along with icon-states and directions (which might have to have a selection for 4 or 8 directions). You could check any of these and it would generate every possible combination of listed values for the selected variables as instances to be placed on the map.
Additionally, anything specified "as num" could also be selected as a range, using a similar format as a for() loop (for X to Y step Z).
Variables not selected would still have an input box to select what value it should be for the instances. It would be a combination text-input and drop-down box, so you could select any of the listed variables but could input anything as desired. Anything using an "as type" declaration (or rather, any fundamental types, "as mob" wouldn't work out) would be available to be specified this way.
Of course, I'm not sure if more than a dozen people even know about the current Generate Instances options, so it might all be wasted effort.