This topic is about GSoC and I don’t think a framework discussion fits in here. Though, I will add my 2c here and focus on why I think React is the best choice that we have right now:
React is very approachable in my opinion. You can learn the React basics within a few hours. It has, by far, the highest satisfaction rate of all JS frameworks (https://stateofjs.com/2017/front-end/results/). I very much disliked JSX at first but I think React got the separation of concerns right (separate by components, not by technology). Vue still tries to separate by technology, same is true for Angular.
We did large projects in Angular 1, Angular 2, and React. Choosing the right framework is no trivial decision and in my experience, the only way to judge a framework is by using it in a real-world project over a longer period of time. Both Angular 2 and React solved their use cases well for us.
If Plone is a CMS for public-facing websites, server-side rendering is a necessity (for speed and SEO). We had some troubles with Angular 2 and server-side rendering. We tried very hard for more than one year and failed.
So personally I would not recommend Angular for public website projects (for intranets it is a very good choice though). I have no idea how mature SSR is in Vue, but I have my doubts they solved a problem that Angular is still struggling so hard with.
Angular has the fantastic SDK by Eric though, so that’s also a big plus if you do intranet projects.
Vue is still new and the React / Angular ecosystem is still a lot bigger I think. Technologies like React Native are becoming more and more important (not sure if Vue has something similar). Tooling and stability are also very important (React 16 was rewritten from the scratch without any major upgrade problems, Angular had breaking changes within the RC).
React is also very close to ES 6 standards, so it is easier to switch between different frameworks.
To be honest, I don’t really want to spend too much time and energy on discussions. In Open Source doing things matters, talk is always cheap.
We (at kitconcept) heavily invested into plone-react in the last months in a client project and we plan to continue to push this further. We will host a sprint soon to push our work upstream.
Working with the Pastanaga UI and plone-react (with SSR) is fantastic. This is the CMS user experience I always dreamed about. We are not where I want us to be though.
I encourage everybody to try out as many new frameworks as possible. It is awesome that we have Angular 2, React, and Vue options for plone.restapi. The frameworks are getting closer to each other, so it becomes easier to switch.
Vue is the hot thing in 2018, so I understand why people are going in that direction. It is also not dominated by a large corporation, which makes it stand out.
Though, I don’t think it matches React with maturity, stability, and ecosystem yet. I think plone-react + Pastanaga UI are our future and this combination should become Plone 6.
Another major Plone release without a modern JS front-end framework does not make any sense IMHO and plone-react is by far the most advanced option we have.
We will continue to push for plone-react and I hope we can convince the Plone community at some point that this is the way to go. Until then, competition and collaboration is what makes Open Source projects thrive.