Imants Cekusins
doesn't seem to be any particular reason to require JS for basic functionality on a documentation site.)
Js is widely used these days. E.g., ReadTheDocs use Js [1].
The fact that JavaScript is widely adopted makes it acceptable to use, but it is not a _reason_ to use it. I don't see anything about the (mostly static) Cabal website that motivates its use. I will discuss that more below.
For someone with basic React knowledge the website is easy to maintain.
This statement sounds like you are volunteering to create a new website, but not to maintain it. Is that what you mean to say?
SPA arch allows for faster navigation between the pages. Client side rendering frees up the server.
In this instance, SPA seems like a solution in search of a problem. There is nothing about the static content of the Cabal website that would motivate using SPA. I find the claim dubious, but let us assume that SPA would lead to faster page navigation; is page navigation too slow now? Likewise, client-side rendering may free up some server resources; is the Cabal website server-resource bound now? To my untrained eye, the motivation for the new design seems to be neophilia. That's good for an experiment, but I don't see the motivation to adopt it. What does this redesign offer to our users? What does it offer to us?