how to make VAADIN and Vue.js coexistent

Currently we have the web application completely implemented with VAADIN 7.6.2

For some reasons we have big lobby for vue.js in the company.

This leads us to the Q:
how to make VAADIN and Vue.js coexistent

we found the possibility to integrate with iFrame

is there another chance we missed?

Yes - you can also embed a Vaadin 7 application inside a <div> element: https://vaadin.com/docs/v7/framework/advanced/advanced-embedding.html

I’d also recommend taking a look at Vaadin Fusion: https://vaadin.com/fusion (possibly together with Vue)