Since you said that you were interested in StructuredDiscussions, I thought I'd move this here. No need to sign, and there's a handy box for adding your reply to this post. ;-)
We did notify everyone with a big banner. After my experience with VisualEditor in 2013, I am not sure that "a big banner" actually works well (and I'd love to know what other people think about that). Back then, I personally posted messages to more than 100 pages, plus banners ran for weeks, and it was discussed on every Village pump and every other central page – and I still had people tell me that they'd never heard anything about it. Some of that may be individual prefs settings (like setting your language to en-GB), but I think a bigger problem is what we call "banner blindness". After a while, you just ignore all those banners. Or maybe you read them, but there's so much going on that you forget afterwards.
If you're curious, the first banner for this consultation ran for a week in multiple languages. The CentralNotice banner brought people to the main announcement, which had links to the list of local pages and links to the main page.
I decided that this might have been too complicated, so on Tuesday, they set up a second banner for me, which brought people directly to this page and ran for 24 hours and only in English (or perhaps there was a French version as well, although that should have pointed to the French Wikipedia's local page, because this page wasn't translated; I didn't set it up).
The consultation has also been announced at in-person events such as EMWCon Spring 2019, and I believe that every m:Affiliate group received at least one notice, so they could invite their members and talk about their group's needs. I've personally e-mailed a handful of user groups that deal with edit-a-thons, and it was posted to nearly all of the Village pumps and multiple mailing lists. I've been told that it's been mentioned on Facebook repeatedly, and on Twitter, for those who follow their communities there. But a way to actually reach everyone – that's hard. I'm always taking notes on how to improve that aspect, so if you've got ideas (today, next week, next year – seriously), please let me know.