[zmj]

> Plus nodes can easily know how far all of them have progressed and drop history before the most far behind point.

That may be easy coordinating servers that are almost always online, but it's definitely not easy for desktop/mobile clients that go offline for long periods (and sometimes don't come back).

[IggleSniggle]

A middle ground could be a combination of "historic" nodes that keep all known history and "client" nodes that only care about history from their own moment of sync onward, the optimistically drop history via some heuristic.