Just a quick heads-up to say that the team decided to implement most of this, but not all of it. Official announcements will be forthcoming, but the overall notion is this:
- They will not disallow all obsolete HTML tags. That could be done later, but they wanted to keep it simpler at this stage.
- Most of the work will happen during 2020.
- After they make the initial changes to MediaWiki, we'll notify active editors if their signatures need to be updated.
- I think that the most likely approach is a MassMessage for each separate problem ("you need to un-tick that box" to one list, "you need to get the template out of your sig" to another list, etc.). @AntiCompositeNumber has a good system for generating these lists, which means that anyone can start this work at any point, or you can wait for me to send messages.
- If you can help with translation and localization of these messages, please watch this thread (click the star in the upper corner of *this* thread to make it blue, even if you're watching the whole page [which I recommend, too]).