I did in fact try to improve the size of jQuery, but the tests are too coupled to the internal behavior of the methods, even if undocumented and (potentially) unintended initially. So it was very difficult even to change the most basic things, let alone change the internal structure of the whole method.
With Umbrella JS I'm trying to get to somewhere closer to native Javascript than jQuery. See for instance the arguments of any looping function (follows similar to the native arrays), or how things like .addClass(name) [1] are thin wrappers around .classList.add(name) (but quite more permissive/flexible). So it will follow closer to classList behavior than to whatever is defined in jQuery's tests, which is a win-win IMHO (since it also makes for a much smaller size, compare to jQuery's .addClass(name) [2]).
[1] https://github.com/franciscop/umbrella/blob/master/src/plugi...
[2] https://github.com/jquery/jquery/blob/master/src/attributes/...