Is screen designer for the document dialogue on its way?

The new document dialogue isn't exactly the same thing as being able to adapt the dialogue in the screen designer, but I see what you mean, maybe R&D doesn't want to waste time adding the old dialogue to the designer when the new one is around the corner

The old/current document dialog is never going to be added to the screen designer. The screen designer is based on the SCIL framework/technology, which the current document dialog does not use. Once the document dialog is rebuild in SCIL it can be added/supported by the screen designer.