Embed excalifraw similarly as draw.io
excalidraw.com is phenomenal whiteboarding app which has been designed for to support in app embedding.
The file format also supports both JSON and PNG with embedded drawing data.
I think this would be a perfect fit for wiki.js. Two stunning open source projects.
Might be a good merge request candidate for someone willing to help the main dev. Probably possible to mimick existing draw.io implementation.