Adding a guild word to each object header is certainly a way to check ownership, and should be a cheap check to perform in the interpreter, but will obviously add some extra overhead to standard program execution.
The thing that concerns me is that explicit ownership passing can introduce as many bugs as it solves. If I have two objects A and B, with A holding a reference to B, then I can freeze A and freely pass it between guilds, but if I try and touch B I'll get an error until that too has been frozen or its ownership transferred. The same problems occurs with explicit ownership transfer of a non-frozen A, which leaves you with the slower option of a deep-copy or a recursive ownership transfer which can have equally unexpected consequences.
The "Ruby global data" slide also gives me the scream heebie-jeebies, as did finding stack overflow answers on how to unfreeze objects in MRI. I'm sure nothing will go wrong. :-)
Having said all that, it probably can work nicely for the common use cases of balancing requests between a group of worker guilds where the request is a simple data structure whose ownership can be safely transferred, but it would be hard to do a general work stealing solution that was always safe.
