In terms of spec, I propose the following change to the settings:

    "com.mattermost.custom-attributes": {
        "CustomAttributes": [
            {
                "Name": ":mattermost: [Core Committer](https://developers.mattermost.com/contribute/getting-started/core-committers/)",
                "UserIDs": ["someuserID1", "someuserID2"],
                "GroupIDs":["somegroupID1","somegroupID2"],
                "ShowBadge": true
            },
            {
                "Name": ":mattermost: Staff",
                "UserIDs": ["someuserID3", "someuserID4"],
                "GroupIDs":["somegroupID3","somegroupID4"]
            }
        ]
    }

where an attribute with ShowBadge = true is visible in all channels.

I can help with a PR for this, but would need some pointers about the best way to implement this. I don't see an obvious option for setting post flair in the plugin registry (https://developers.mattermost.com/extend/plugins/webapp/reference/#registry)

Presumably it would make a lot of sense to hook into the code that generates the [BOT] badge for posts from the API.

Instead of a boolean for ShowBadge, would it make more sense to have the variable hold the actual badge (e.g. "ShowBadge": ":star:") ?
This would allow customizing the icon or text to be shown.

Perhaps unnecessary but I would also consider "BadgeLocation" : "left|middle|right", to have the badge positioned in one of three locations: (left) FirstName (middle) LastName (right).

We're also interested in this!