Backdrop Core in reality isn’t really a framework framework in the first place because it was more for me to re-organized files and where to put files in a good location so that it would be easier to grab when working a theme for development for WordPress.
So I needed to create something that would help me develop a theme at a faster pace because in reality again, every feature that I have created so far has been the same thing over and over again. This is where Backdrop Core came in play.
All of the features and supports that will never be change should be part of the framework. if you need to tweak in anyways, it shouldn’t be part of the framework but in the theme instead. The framework is just meant for me but anyone can use it, but I haven’t really put together a wiki yet because things can change.