ill keep my user friendly ideas to myself in the future.
open source, ratty community
User friendly is a really terrible term. Most people take it to mean "like the other software I've used" which really discourages innovation or efficient UIs.
This idea would also do nothing but encourage people to do it wrong. There are a thousand ways to install a library incorrectly. Most of them don't work at all so people don't do them. Others work but are not supported, so people do them and then complain they're not supported. Even worse are the people who do it the wrong way that works correctly and then tell other people to do it that way. It's best in software development to dissuade people from doing this rather than having to support this "feature" forevermore.
There's also not too many people interested enough to design a cross-platform solution to your idea and they're generally busy doing other things.
Finally, and most importantly, arduino 1.0.5 implemented an auto-install feature which does it right for you.