I was thinking about this discussion in the context of phab:T344067 ("Gadget icons may go missing - how to fix") -- TLDR: that task affects ~45 gadgets (most of which are copies of a single specific darkmode gadget) and ~45 user-CSS pages. When we added that to Tech News, it frustrated me that thousands[1] of people were likely to read something that only a tiny handful of people can help with.[2]
For a task like that, I think we essentially want a way to reach some specific Interface Admins (IAs). It isn't practical to manually construct a custom MassMessage target-list for each time something like this occurs, especially as we want to be more communicative (higher quantity) about things like this (and hence related concerns for just using Tech News to do it). We also want to avoid making the signal-to-noise ratio even worse at smaller wikis' Village Pumps (phab:T130602 et al).
I'm not sure if a new mailinglist is a practical solution, unless we require subscription. (and while IA's are required to have 2FA, I don't believe that 2FA requires a registered email, so Tacsipacsi is correct about that concern, as well as the privacy concern.) And even then it wouldn't reach userscript-devs who are almost impossible to comprehensively list.
For the narrower use-cases like my example: We've linked to GlobalSearch a few times in similar tasks, and I wonder (pipedream?) if it would be possible to use results from that, along with the {{ping}} feature, via some kind of simple scripting? -- E.g. Perhaps it's possible to hack together a quick tool that matches "wikinames from GlobalSearch results" with "complete list of all IAs on each wiki"(?), so that if we wanted to contact the IAs from (xxwiki, yywiki, zzwiki, ...) we could get a copy & pasteable {{ping|alice|bob|charlie}} that any dev could then easily use in a talkpage post on m:Tech noticeboard, and use a page like that as the central location.(?)
Overall, the choices are basically: Mailing list, Onwiki broad announcement, Onwiki targeted message, Onwiki centralized ping. All have many pros and cons. They could even be combined, e.g. "new announce mailing list, + manually copy it to a centralized noticeboard".
To get any further with this discussion, I think it might help to have additional examples of the kinds of content we'd expect to be communicating, so that we can think about the target-audience more clearly. I.e. Beyond phab:T344067 and phab:T303488.
I hope these thoughts help! Sorry for the length.
[1] (Tech News currently reaches: ~300 notice-boards and ~700 individuals onwiki, plus ~900 Diff-blog subscribers and ~600 wikitech-ambassadors@ subscribers)
[2] (even fewer people than the usual small-ish quantity likely to be interested in any average Tech News entry, as Tacsipacsi notes.)