Well first yes it's been tested: that's how email, DNS, WWW, XMPP, Matrix (and others) work. Heck, that's how most of the Internet works! But also, maybe the p

Well first yes it's been tested: that's how email, DNS, WWW, XMPP, Matrix (and others) work. Heck, that's how most of the Internet works! But also, maybe the problem is we often develop apps as a fragile monolith which is definitely not intended to be customized in terms of UI. When the core or your application is designed library-first so that your executable is only an opinionated wrapper (client) around the lib, you make it easier for others to reach their usecase by implementing a different wrapper. I don't see a reason this wouldn't apply to composable/reusable GUI components: early Mozilla (XUL) is a famous example of that.