A very well written overview of when client-side functionality and server-side functionality make sense to use for a website.

Frustrating to read, though, because not only have people been saying this for years (and saying this to the author, in particular, for years, which is not acknowledged here at all), but they've also been solving this for years. There are many competing patterns out there, so I wouldn't call this a problem with a definitive answer. But positing the question and then effectively shrugging your shoulders and saying "but who could ever possibly dream of such a world" is a little trite when solutions do, in fact, exist.

Though is it trite, or is it simply worrying that someone who has supposedly been thinking around solutions to this problem themselves seems so unaware of the space they are considered a thought leader within..?

For example:

Is there some way we could split components between your computer and mine in a way that preserves what’s great about React? Could we combine and nest components from two different environments? How would that work?

Yes, Islands Architecture. Or Web Components. This is neither a "hard" problem (at a conceptual level) nor an unsolved one.

(Though perhaps the issue here is the "preserves what's great about React", because based on React's attempts to solve these issues, I'm not sure the React team and the general developer community agree on what that is.)