Part of the reason I like my proposal is because it's just a generic server URI, so deeply familiar to nearly all developers. And for that format, it's the GET query string that allows for additional parameters.
Yes, but for convenience (and compatibility with other proposals), I think it would be okay for a given implementation to recognize well-known engines and treat them as valid DB URIs even in the absence of a <code>db:</code> prefix. I've added notes to the <a href="https://github.com/theory/uri-db">documentation</a> to that effect.
This blog post is soliciting feedback on the general idea before I go and do the work of submitting a formal RFC. For all I know, someone could have shot it down. Just think of this as step 1 toward the development of an RFC.