To me, the next generation of PKM doesn't lie at the level of representation but at the level simplification, and integrating prior strands of though into something usable.

We leave such data trails, but every time we switch or another tool comes along, the switching cost/conversion process leaves much to be desired and some of our prior history beyond reach.

Even as plain text, the sheer feature discrepancy between tool A and B leaves our knowledge siloed. The semantic Web had its moments, but we never took that concept to heart when considering our individual webs of thought.

Your semantics and mine may be inoperable, but that's okay. We just need better tooling to accustom our personal semantics, and I think projects like this lay the groundwork for that.