Thanks everyone for all of the thoughts here.
Tom - Given that some extensions are already depending on these changes, I wouldn't expect them to change any time soon. I definitely appreciate the concern and frustration though. I totally understand waiting for our next update and hopefully when we share that it'll help to give you a better idea of what the rest of the transition will look like.
Vardhman - I completely appreciate the concern that other extensions may be hitting these. I don't think there's much more we can say on that, because without reports there really isn't anything to go on. But we definitely keep an eye on the bugs being filed (from both developers and end users) to get a feel for things. For that bug specifically, my understanding is that similar behaviour has been reported in both MV2 and MV3. It may be that the extensions you looked at are yet to attempt the migration but are still hitting this in MV2. It does seem like there's enough activity on that bug that it would be reasonable to think about adding it to the known issues doc. That said, the fact that it isn't MV3 specific might be an argument against that. I'll ask the team about it.
Simeon - Thanks for sharing that, I completely appreciate the situation you're in.
Do keep the feedback coming, we really appreciate it. I realise that it's frustrating that some of these issues take time to resolve, but we are focused on doing that.