I'd like to see an ability similar to /window -h @window, but for modeless dialogs (although /dialog -h is already used), because hiding a dialog without having to close it would be really useful.
Ofcourse, one should be able to bring the dialog back too

Well for now you can use MDX with a control called a positionner that lets you hide/show a dialog.

Move it off screen with /dialog -s <name> -500 <y w h>