You might be interested in taking a look at Graft (https://graft.rs/). I have been iterating in this space for the last year, and have learned a lot about it. Graft has a slightly different set of goals, one of which is to keep writes fast and small and optimize for partial replication. That said, Graft shares several design decisions, including the use of framed ZStd compression to store pages.

I do like the B-tree aware grouping idea. This seems like a useful optimization for larger scan-style workloads. It helps eliminate the need to vacuum as much.

Have you considered doing other kinds of optimizations? Empty pages, free pages, etc.