This is what you recommend for C3 plugin makers: "I think there is some level of responsibility for addon developers to keep an eye on developer news, release notes, listen to feedback coming from users, and maybe do a quick test every couple of months". Actually you also said that you gave a heads up three months before a breaking change to C3 plugin makers to fix their plugins when you did breaking changes.
But to be fair, Google gave you one year for this one. You also have the same responsibility to look into the release notes from Google every now and then, just to check if some small tweak is needed. Now when you didn't do anything for a year I understand it's a huge job to do it all in one go. But the UMP was really released July 2020, same time they marked the old EU consent to be deprecated.
"If nobody is developing an addon, it will probably break sooner or later.". They also gave out a guide how to amend the ad methods to comply with v20 release (several months before removing the old methods!), but you didn't amend those either. So then the plugin broke..
I know you are a small team and all, but unfortunately this plugin needs proper attention. You seem more interested in building your 3D boxes and such at the moment, but that is just not a good priority at the current state.
Maybe the Admob plugin would be a good one to have external help with? Maybe consult Iain or some plugin maker to write the first version. But you must have ownership, and interest in it.
But good that this finally seems to get proper attention. Thanks!
My suggestion is a new one, and deprecate the old one (so it cannot be imported in any new project), but for old existing projects you should be able to maybe have them both, so you can amend the events before removing the old one. Obviously only have the new one when you export! But since it will be many breaking changes I think i will be hard to rewrite the current one to get all ACEs to work with the new stuff. (But do like you did with Function-plugin sort of).
Good luck! Looking forward to it.