https://gist.github.com/AdamISZ/b462838cbc8cc06aae0c15610502e4da ?
That was an interesting read. The single biggest limitation is probably the inability to "skip" part of the path. Otherwise you could repeat the same participants M times, to get arbitrary transfers (with an eye-watering (M * N)^2 efficiency lol).
I was also thinking a bit about spend efficiency, you can probably do better than tap-leaf-per-case (which wasn't explicitly stated, but sort of implied) by compressing multiple CSVs into one tap leaf.
And then finally, I wonder if the "vertical" portion of signature sharing could be compressed by pre-sharing them all, and having some adapter which is constant between them? (guy with only a vague, intuitive understanding of signature adapters)