It should be optional, if I understand the design principle of V2. My reading of what Jethro was saying is he wanted to treat files and headings in a uniform way. Org-ID would let Org-roam code achieve this. The org file section before the first heading should be treated as if it was level zero heading.
You can also set tags that all entries in a file should inherit just as if these tags were defined in a hypothetical level zero that surrounds the entire file.
So, you set variables org-use-tag-inheritance and org-tags-exclude-from-inheritance according to your needs, right?