I liked the compromised you took when dealing with this problem.

I have worked in the past with these issues and my opinion is that it is the "usage" what dictates what's better.

- path-based hierarchies are *NOT* slow for many kind of queries but they *ARE* for some others.

- Nested-Sets are *NOT* good as you already pointed out for changes BUT also certain queries are "hard" to craft.

- The Built-in hierarchy-ID of 2008 is basically a path-based method that happens to be in binary representation and it has many (almost all) the drawbacks of the pre-2008 forms it just operates faster and it does not have as many limitations as a varchar column.

All in all I think you put together an interesting method.

Great work!