Adding jQuery [type] functionality to the browser's in-built JS implementation (or making it a 1st-class plug-in) would overcome one basic problem:
As many have said, jQuery is a JS library - meaning, in case the penny didn't drop - that it is written in JS and has to be interpreted at run-time.
Embedding it would mean that it could be written in native code for the OS, making it much more performant.
