I think this might be too simple. In particular, the absence of a way for the client to specify a desired language or supported mime types, query strings as the only way for the client to send data (what about uploads? Or non-idempotentent requests like registration?),and the absence of compression all seem to go a little too far to me (compression could be done using a parameter to the mime type).

And really,why replace http? The complaint seems to be mostly with html, so why not just makr a gemini text format,build some browsers that use that as the default instead of html and specify semantics for how tls works, like custom status codes to request a client certificate and recommend TOFU certificate trust. And maybe specify certain headers that shouldn't be used, like cookie.