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!