It's a thing you can do. But it is very bad for extensions and extension developers for the same reasons that Java applets, Flash, and Shockwave were bad for the web. These apps are difficult for end users to customize. It's a real bane to tinkerers. And it's a shame that "view source" has slowly grown completely useless over the decades.
[1]: https://workspaceupdates.googleblog.com/2021/05/Google-Docs-...