This seems like a solution looking for a problem. The problem isn't that people doesn't have armbands to do stuff they should be doing, the problem is that those actions aren't explicitly allowed, but instead implicit allowed. Examples:
- curators: all those things are implicitly allowed by the editing, voting and bounty pages. There's no rule that says that you can't coordinate with others to make sure questions get the attention they deserve and the [tag]?tab=Frequent gives you an overall view of what is the most frequent questions on the tag (btw, please make that tab more prominent/default).
- tag curators: is just a rehashing of the gold badge privileges, which I personally think should be expanded to all close reasons. It's nothing new.
- audit moderators: we have the power of removing a bad audit via simple voting, difference here is that we have to be aware of the bad audit first.
- mentorship: this is trying to funnel users towards a staging state, SE has more information about this than I do, but I don't think an armband would help here. This is structured guidance rather than unstructured, and should be done one on one, the public site isn't optimal for this.
- migration helper: is merely a lack of coordinated voting, since those small tags that have their own site members don't come often to SO. Chat rooms help here.
- Tag Manager and the others like it: this is mainly a request for better tools to manage tags and the creation of a guidance about "what should the tag corpus be" rather than a lack of roles. I already made proposals for the tooling aspects, which I will not rehash (mainly, bulk add/removal).
- Translation Reviewer: afaik, this already exist, it just doesn't get an armband. Also, any community member can report mistranslations.
- Global coverage champion: this can already be done by users, they simply aren't that interested.
As you can see this is not a problem solved by RPG'ing our way to victory. It's merely a human problem, and in some cases a lack of adequate tooling. If you fix the later, the former will be easier. Also, I have a general distaste of armbands because if someone tells me that I can't edit a question because I'm not a curator I will be very mad. Also, you have to consider the confusion aspects of it for external users (the 99% of the users that use the site). They already have problems correctly identifying the difference between a moderator and an user that can edit/close/vote/comment, adding more on top of it, will only cause more confusion.
I propose this: get devs cracking at better tooling for stuff that is needed, update the help center to have a non-exhaustive list of allowed actions (and explicitly tell that is not exhaustive too, this is very important), and try to give guidance so that humans can coordinate better. Multisite chatrooms could help?
