Having worked extensively with the existing Calendar control (Vaadin 7 based), and given that:
I propose the integration of a custom component based on this JQuery plugin: https://fullcalendar.io/docs
It is MIT licensed, has extensive and detailed API docs, it is easily themeable and extensible, and constantly improved and tested.
Such a great JS component will give a wealth of capabilities way beyond any other current (and I think future) Vaadin component.
If you’re interested, please share your opinion and vote for it. I’m considering to start working on this ASAP, and release it to the public if there’s some interest in it.