If I'm reading this proposal correctly, locks will still be needed within multithreaded guilds to guard mutations against complex object graphs.
Here's my reasoning. Since the GVL is insufficient to guard against data races on Ruby 2, under the guild system, locks would be needed to guard against concurrency issues if multiple threads are present.
It would seem like the intention would be to replace usages of Thread with Guild to avoid the concurrency issues inherent with threaded code. Will there be API support to create a Guild that only allows a single thread?