I think the ability to have multiple Tabs in a dialog would be nice. You could use the group style to separate tab sets. Something like this:
dialog dname {
  size -1 -1 500 400
  tab "Set 1 Tab 1",1,0 0 500 200,group
  tab "Set 1 Tab 2",2

  tab "Set 2 Tab 1",3,0 200 500 200,group
  tab "Set 2 Tab 2",4

Another thought is a canvas control, it would be similar to a @window but would be a control id that you could draw on with the /draw commands.

What about modifying dialog controls. You could have the following commands/identifiers to modify current dialog controls
  • /mdid -a to add a control
  • /mdid -d to delete a control
  • /mdid -m to move/size a control
  • /mdid -s <dname> to change the control styles
  • $did().x
  • $did().y
  • $did().w
  • $did().h
  • $did().control
  • $did().styles

Any control in DCX would be nice.