This vis.js library seems amazing, after looking at the screenshots and some examples.
Take a look at this pages about where to place code, or how to create Wiki Plugins, etc.:
But I'm afraid you will not be able to add it to the Tiki main codebase, due to license incompatibilities, I guess.
According to this page, vis.js uses Apache v2.0 License:
And according to this other page, Tiki uses LGPL 2.1, which doesn't seem to be compatible with Apache 2.0:
And/or request some license change or dual license to vis.js or to Tiki, I guess
Regarding Tiki license, the best place to post the question, is the "Development" list:
Keep up the good work you are doing!
(I'd love to use your vis.js plugin!)