Several community members have been busy creating a lot of gallery pages for subnational flags, some of which have had unproductive edit conflicts over what flags they should include or whether to delete them. Although I understand the desire to make a page for every country, I would advise slowing down until these are resolved.
This post has gotten pretty long, but hopefully elaborating on some of the general issues will help in finding some agreement on what to do with these types of pages.
Firstly, proposals and other unofficial flags are very much allowed on the wiki, being what it was originally created for. We are also not subject to any government except the US's (since that's where Fandom is from), so flags being illegal or taboo in other countries isn't, on its own, a reason for deleting content.
That being said, flags shouldn't be presented in a way that is misleading to the reader. If someone finds a gallery page named "Flags of regions of X", they would probably assume it contains "real", possibly official flags. Even if a flag is marked as "(unofficial)", including it at all implies it is in actual use to represent a region when it might not be.
Proposals generally don't belong in such a gallery, nor do flags that probably aren't legitimate (try finding and linking a reliable source if in doubt). Also, if not official, the necessary context should be given in the image caption if possible. (This all holds not just for galleries, but for any place where a "real" flag would be expected, such as in infoboxes and navboxes.)
What this means for the pages in question is up for discussion. Gallery pages of "real" regional flags can definitely be valuable for the wiki, if only for navigation between subdivision articles. Some things to consider, though:
What counts as a "real" flag? I don't think only official flags should be allowed in galleries, since there are plenty of well-established local flags that haven't been formally adopted. I don't have a good criterion, though, and it's often a challenge to verify whether a flag is actually official or in use.
When does a country need a gallery page for its subdivisions? If only one or two regions have a flag, and there's only a placeholder image for the others, then it might not be a very useful article, and a section in the main country article (if anything) might be enough. This is particularly relevant to the recent conflicts on the Oman and Mozambique pages.
Also worth discussing, given the number of pages involved: the titles and structure of the pages. For example, a lot of them seem to use Commons gallery formatting templates, whereas most of our other articles use the standard <gallery> tag. As for the titles, there isn't really an established naming scheme for this sort of page. I'd personally suggest something like "Italy/Subdivisions" instead of the current names, but others may have different ideas. There are no rights or wrongs here, although consistency between articles is a good thing to aim for.
As mentioned before, flags that aren't "real" are still welcome if posted in the right place. Some of the pages that contain just proposals have been moved to titles such as "Proposed flags of regions of X", which solves the main problem of misleading readers. Although it's not the usual format for proposals in articles (which would be a separate page for each region), I think it's a good one when there aren't any current flags.
I would ask to avoid pages focusing on a single set of proposals, though, and instead use a structure like that of the Iran page, with a separate section for each region. That make it easy to add new proposals without making the gallery unmanageable.
