There’s no fundamental reason ISS modules couldn’t autonomously dock with each other. The main reason it wasn’t entirely built that way (though some sections definitely were) is because of the desire to create a PR justification for the Shuttle. In fact, modules have been added to the station since the Shuttle went out of service, and will continue to be added. Anything that couldn’t connect that way you could install onsite using EVA by ISS crew and the ISS Canadarm, which is a level of capability you could easily reach by launching autonomous self-powered modules.