Is vizjs integration at https://github.com/plantuml/vizjs in usable state? viz.js has been improved quite a bit since its early days, so I'm curious if upgrading viz.js and J2V8 to a newer version would yield nice results.
According to http://plantuml.com/vizjs:
For complex diagrams (especially with labels on arrow), the solution is not working very well.
An issue has been opened on viz.js side (see Error when generating graph).
However, the linked issue seems to be resolved long time ago.