So basically if we create a "Master(s)" subdomain we should be able to just attach it/them in our profile and use it/them as a drop down option when publishing to domains.

So for example subdomain 123.website.com and when chosen and new page when "published" would be 123.website.com/name-of-url

this would make it easier than each having to be a subdomain directly of its own and going back and forth with DNS.

Now you could still keep the manual entry but maybe if it recognizes that there is a "master" subdomain you put into the "publish to subdomain" popup it could gives you the option to just publish directly to that and creates the url while still giving you the option to say "no" and still go through the steps of adding a new subdomain directly if that's what you want (like it does now).