Like you, I've played with it many times and am always intrigued by this idea of handling sparsity this way, but I just end up backing out these changes in the end because it never seems to pay off like my geeky fantasy plays it out.

The LeanStore and Umbra DB buffer pool management systems intrigued me. I even got paid to work on a system like this (buffer pool at an analytical database company). The KISS data structure (https://dl.acm.org/doi/10.1145/2236584.2236587) and the START adaptive radix tree (https://db.in.tum.de/~fent/papers/Self%20Tuning%20Art.pdf?la...) have also intrigued me. I've been very intrigued and almost always disappointed.

In practice performance gains have never really materialized for me ... I do think there are wins to be had here, but only for specialized cases.

And just watch how confused and annoyed your users are when they see an absolutely huge VSS. Sysadmins freaking out at your "insane memory usage" (which is really only on paper not in reality). And the difficulty of profiling or tracking what's going on easily.