Trying to catch up with all the posts here… it’s helpful for my understanding, thanks! But I think @hostilefork has covered everything I would have wanted to say.
One of my original thoughts was that environments could be first-class values. Then BIND would simply bind an environment value to a block. But, since it now seems that functions can be used to do most environment manipulation, perhaps this is no longer needed? (Though I still think it’s a good idea.)