Thanks! Ren-C is a mess in lots of ways...but it's held together by some fairly robust defensive coding strategies, and bends pretty well to new ideas.
I had actually forgotten how much of the first attempt had been committed in bits and pieces as groundwork. Thought I was going to have to go back to the old branch to merge bits in, but everything uncontroversial was already merged in some form.
Seems reasonable to see if there's any insights. In the past I've briefly looked at stuff like Hidden Classes in V8, and there's a lot to consider if you are looking for speed at the cost of other things.
Though one goal is to try and keep the implementation as simple as possible. It's painful to write something like this in pure C and not have things like the C++ standard library... but it makes you think about alternative ways of solving problems.
Moved discussion to Optimizing Environment Lookup