I know it's not the main topic of this article, but just to toss it out there, I have had really good luck with the Shadow DOM, but for a different use case of custom elements: "Late-as-possible FE Integration" For big chunks of UI representing features that reach meekly into another feature (think: comment threads+form on an article, or background process status widget), that are managed by another team and/or needs to integrate into many different front end apps with different architectures, the inflexibility is rather helpful.

The things that make THIS specific usecase a great one for Shadow DOM makes it awful for composing small custom elements into a bigger application. I agree there. But for gluing together entire features...

- You keep styles separate, so impact from an accidentally shared CSS rule is limited. This is a huge plus when you consider this other feature can be deployed totally out of sync with your hosting-application. They're feature is just some HTML/CSS/JS accessible internet, not a package.

- Events are neatly rewritten when crossing the Shadow DOM to lightly enforce a public interface. (The feature needs to emit events, don't rely on listening to a button IN another feature.)

- Issues with ARIA/AOM are generally limited if you commit to it being the integration medium: just 1 Shadow DOM root per big feature. That way references are at least scoped naturally to this chunk of the document. If something truly describes/controls something specific outside of the Shadow DOM, then IMO, it's not an independent feature. A feature should work generally on the current resource the URL represents.

- And best of all for my use cases, it can go anywhere HTML is. For strangler fig pattern refactoring [0], it's a massive help. Migrating by-feature rather than by-page speeds up how quickly the value of a refactor can be demonstrated.

[0] https://en.wikipedia.org/wiki/Strangler_fig_pattern

EDIT: Just realized the author just wrote about that, yesterday! https://gomakethings.com/no-seriously-the-shadow-dom-sucks/#...