I think adding this to core in the specific way requested here would add significant HTML bloat sent to all users that contribute, and give us a very difficult, narrow, and expensive API to maintain for almost no public benefit.

The idea of indicating visually who is priviledged on the wiki is questionable by itself and something Growth-Team may want to think about. Even this is not really a means to an end, but merely a tool for a larger user case, which is worth understanding and perhaps solving properly. For example, is it about curation/review during diffs? Or about trust in discussions? Or about the fact that our history page is so hard to use and to find when vandalism was added we have to go through 100 diffs and these might help you intuitively skip unlikely suspect? The fact that there are so many uses for it does not (in my opinion) justify its existence. It just means we have a lot of poor interfaces that need improving for everyone, not just a few people that came up with a creative workaround that is unusable for most people but happens to suite them during the years that we continue to ignore those problems at WMF.

The use during diffs is largely obsoleted by RCFilters / WatchlistFilters, and can be improved upon further there as-needed. If some of the other uses we think and can agree together are beneficial, we could pick up some of those and add that to the subset of links where we want to show it, explicitly and narrowly tied to the display of an icon or symbol. Not generalised. It could internally (not in the HTML) be generalised/configurable to e.g. iterate on what symbols to show and for whom etc.

I will also note that there are numerous workarounds for this that seem pretty good as-is for the handful of people that want it, which is presumably why this task has seen no activity in 8 years. The workaround is generally that a bot or person updats an array of user names inside the gadget script, and use that to add the symbols. This list is based on an API request to fetch admin users. This is essentially an optimised build step and seems ideal in terms of cost/benefit distribution and speaks to the flexibility of the gadget ecosystem. Doing this inside core is imho worse for everyone involved (readers, contributors, gadget authors, core devs, oppertunity cost for WMF).