Just got it working with the Announce/Retire/Update notifications as well- the problem is really that there isn’t a good way to perform a C# callback in unity from C++ plugins.
The way I’ve been dealing with that previously is just polling a bool that represents ‘did something change?’ that is triggered by the KVO. This is not very explicit, which is a shame, as I’d like to perform different tasks in Unity based on whether it was an Announce/Retire/Update, while at the same time performing the least amount of C# -> C++ interop; this is more a design issue than a code one i suppose.