We are doing some fundamental changes to how diagrams are rendered, which would enable us to support more renderers. This will enable us to do server side rendering without a browser.
The main reason why we need a browser currently is size calculations of the SVG boxes, which libraries like jsdom does not support.
Please don't take the, in my opinion, excessive criticism to heart. Mermaid is fantastic. It would be even better if it supported more renderers but as it stands to day its an invaluable tool.
That I can bring GraphViz into a browser but not Mermaid out of the browser forces GraphViz for some usecases. Unless browser-native was the intent (idk, it could be... maybe thats why it was named Mermaid), I do think it should be a high priority thing.
FWIW I gave up trying to render SVG for our project and switched to using fabric.js (and node-canvas for server side rendering). For us it was mostly because it had far better text support.
The main reason why we need a browser currently is size calculations of the SVG boxes, which libraries like jsdom does not support.