I just used Vis.js for graph visualization without much tweaking. There is also a graphviz visualizer that is not optimized for being stable [1] vs [2]. I would gladly accept any improvements here! Please reach out if I can help you.

Implementing custom visualizations is super easy! See [3] for a very simple example. If you implement a visualization there, it will be available for all people that use the visualization framework (e.g. extensions for other IDEs), not only this extension.

[1] https://hediet.github.io/visualization/?darkTheme=1&state=XQ...

[2] https://hediet.github.io/visualization/?darkTheme=1&state=XQ...

[3] https://github.com/hediet/visualization/blob/33de54d69624e1d...