Quite frankly I wrote this more like an exercise. I have never used it in practice other than the github test. I saw people picking up on the other post and didn't really like the indices going unbounded. Then I spent a few minutes thinking how to solve it.

While I think the implementation per se is not that useful (I agree with you), I believe the actual trick can be reused in a different situation or type of container.

Check out the github repo now, I added a choice of allocator. That is nice because the main use of this kind of tool is when you have a slab of mapped memory that you go partitioning.