As of current the toga-cocoa library and from what I see of the other libraries, do not have enough in them to dictate this, but I have been committing to the toga-cocoa branch here (
https://github.com/gabrielcsapo/toga-cocoa).
A thought came to me about what if toga had the capability to have a package manager of some sort built into it, this is wildly far fetched, but I think it would give the toga library a huge step over most gui libraries. The idea would have to be thought out a lot more than just this idea, but I think this could be a step in the next direction, having the ability for developers to make widgets combinations that are themselves native, but are built for a specific purpose.
One example of this would be a package that allows the integration into the OSX system bar. I have been looking for the easiest way to build system bar applications that would help my productivity ten fold.
Wonder what everyone thinks about this.