I recently asked this question: Do I have to maintain two versions of website when I want to use AMPed version on mobile?
I'm curious, what if I'd have only AMPed version of website for mobile and desktop? Do you know any downsides of this kind of solution?
I don't read any downsides of using only AMPed version on websites. As @noogui stated on your previous question, you'll just only need to maintain the two versions if you think that some of your features like third-party JS will not run. Many web pages were migrating to AMP because of the benefits like Faster loading page for mobile users. You can see more information on this FAQs page. You can also check with this Pros and Cons of Google Accelerated Mobile Pages (AMP) blog.