This new function looks very interesting. But what can it do actually? Do we need to know some scripting language, or does it only enable us to build some elaborate dialog boxes, using own commands?
It's for scripts.
Scripts can add commands which display dialogs when you run the commands, so the feature will allow script writers to create new things which anyone can use without scripting knowledge, but you'll need scripting knowledge to write the scripts.
I can´t script, but it looks very promising.