I try to empathise, I really do, but I don't see how this benefits us as C3 users.
I always looked at addons as the "if you can't do this in events, then an addon can get around it".
But this SDK change would be more like "if you can't do this events, and if you can't do this as an addon, then either change your vision for your game, or submit a suggestion and wait X months/years to maybe see it accepted or rejected".
I have always had a good time dealing with addon devs, very quick to fix things on a new C3 release, and also this grows the community as there are wonderful addon devs that feel proud to serve the community.
Even addon devs that left, like with ProUI, the community worked hard to contact them and they kindly open sourced it and now it's being maintained by the addon devs of this community.
I have no clue who will take on porting ProUI, or if they even can. I don't use this personally but it's a great example of how hard working the addon devs are and how much they care, but it sounds like it is inevitable that their hands will be tied entirely.
I wanted to look at skymen's FMOD plugin soon, but now I have no idea if I should risk it. Infact thinking long term, I don't know if I should be removing all addons from my project for safety. Whereas over the years, if an addon broke, it was usually fixed before I asked the addon dev.
Was also thinking to pay addon devs for specific things, but again, I have no idea what to do anymore.
I think the best thing that could happen would be a major change to how suggestions are handled. Then the whole "this is impossible to achieve in events or the new addon sdk" at least has a chance. But I understand Scirra's position and small team and such, I don't see this able to be changed. Suggestions are a luck based time based thing, can't save some money and pay Scirra to make a suggestion (but we could save money and pay addon devs).
The absolute top fear, is, there's not a big addon dev community for C3, and I pray they see positivity in this sdk change and find value in it, rather than them giving up.