Yes, trunk is very alpha right now. Yes, expect breakage.
These aren’t “bugs” in plugins per se. At least not yet. For now, plugin authors should be alerted to follow #21767.
We’re not jumping to revert things as @ryan and I want to take a wait-and-see approach on this. By going all-out initially, it provides us a lot of data to help us plot a modified course of action. We’re working to compile a list of grievances, so please, if something you were doing broke, please post specific code to #21767. We can then make adjustments to avoid major compatibility issues.
We strive to remain compatible from version to version, but sometimes it just requires dropping a commit bomb to see how certain changes will actually play out in the wild. Thanks for testing, and no need to panic. We’ll clean this up before beta. Bear with us, and help us out if you can!