It might be possible, with some hacks, but definitely is not built in and nothing I would encourage. Modules configuration is global. Enabling and disabling them is often slow, as no one bothers to optimize something that is meant to occur once in the lifetime anyway. So allowing this would kill your performance.
Second problem is cache. Proxies can, and often will serve responses from cache, even redirections. So your site might not be able to even know what type of browser accessed it. It might be unable to even notice it is accessed.
Last but not least, if search engine robot detects you serve it different content than you serve to it's clients, your position in result will go down the drain. They are pretty good at detecting changes in theming, but different module sets are only needed if you want to generate actual content differently, or to decide if to perform redirection. Both actions are no-go for SEO purposes.
TL;DR : Probably possible. Don't do it.