I've been looking for a SSR solution too.
Seems like React on Rails is doing SSR somehow. https://github.com/shakacode/react_on_rails/blob/master/docs/additional-reading/server-rendering-tips.md
Another resource I found is the Official Documentation for SSR in a Non-Node JS environment, however Webpacker runs on Node so, I'm a little bit confused.
As third option, I found InertiaJS: https://github.com/inertiajs/inertia-vue inspired from Turbolinks but with VueJS. Right now, there is no Rails version, only Laravel, but the fonder sustain that it can work on Rails, Django and other frameworks...
The last solution I found is Quence Vue https://github.com/stowball/quench-vue
Where you can add Client Side Hydration but the structure is pretty weird.
Posted in How do drag and drop builders work?
I can point you to 2 different open source website builders, they have a starting point but unfortunetly one is made with React and one is made with Backbone Js, and I wanted something in Vue Js.