The standard library base is huge... they already split things into a desktop and full profile for the .Net installer. This will only need to include those portions of the library your app actually uses, which is generally a pretty small part (including GC). Not to mention future versions of the .Net runtime not needing to be installed on the target machine.
Are you sure? You still need the standard libraries, a garbage collector, its security checks when loading other code, and may want to use its compiler from your code. Together, that's a lot, maybe all, of what's in the framework.