Thanks for the issue. I thought about it. But someone could use Symbol.for('observable') for anything else and it will unexpectedly make objects with this property observable. However, sure, it could be solved by using something like prefixes. Also, it will not work with polyfilled Symbol - the proper cross-realm Symbol.for behavior can't be polyfilled, so we could forget about, for example, IE11 - that was the main reason why it's still not added.