I would agree that building a distributed architecture that achieves this is a distraction for most solutions- oriented teams. Before you get to the benefits, most/all teams would drown from the complexity.
Client side interactivity without network delay is a valid use case for these libs. Client side encrypted data also.
It's a surprise that there is no robust backend library that does graph layout.
There's even a d3-node package available to generate a static SVG or png.
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Additionally, grouping or binning the data may be something to consider when dealing with a visualization with 100+ nodes. Never tried that with DAG datasets, not sure how that would work, but it's interesting to think about.
Also agreed on subsets. About 1-10M nodes can still work in the frontend (and we're pushing upper end of that). But around 100K-1M nodes, more about seamless & interactive abstractions... and reinforces why integration w/ smart backend matters.
So the ideal library should be running the layout on the backend and the frontend should be plain dummy, simply showing each graph node at the position co-ordinate sent from the back-end.