Not only could you, but some of us even did (though it definitely was never, as you say, "taken seriously"). What made it super powerful (and very node.js-like)

Not only could you, but some of us even did (though it definitely was never, as you say, "taken seriously"). What made it super powerful (and very node.js-like) was combining it with Jetty, which was a servlet engine that could be used as a library. My (trivial, personal blog) website is still running with this stack (though I finally put it behind an nginx SSL terminator as I have been putting off upgrading Java and Bouncy Castle just couldn't keep up), and it gives me more warm fuzzies than v8 alternatives. A "people actually used this" framework that had Rhino at its core (well, in one of many ways of using it) was Apache Cocoon (which was maybe more by-default based in XSL/T), only they did something almost ridiculously clever: as Rhino had full support for continuations, they didn't need "callback hell" (or async/await) and could even support pseudo-synchronous code that could block on the user (such as a function which sent the user a form and returned the user's selection, possibly hours later) by storing the continuation state in the user's session.