Why would accessing the registry take more than a few milliseconds? Pre-8.x, you'd get a run-time error if you tried to access the registry from outside the main or task threads. That error is gone, so I'm assuming it's ok. I'll deal with the ramifications if/when they occur, but I'm using the registry as a simple way to pass setup information to my components (i.e., not for communication) in my most recently published channel.
Roku's documentation has always trailed reality by months if not years.