Sass is here. Finally.
Bootstrap 4 is moving from LESS to Sass!
In the early days of bootstrap, we had to rely on outside developers maintaining a port of bootstrap in Sass so that we could integrate with our existing Sass projects. It got better with Bootstrap 2 and an official Sass repo. But it always felt an after thought and you would get some strange problems every once in awhile as the main developers were lax in focusing on the Sass side of things.
This is great!
There is a lot of good stuff coming in 4 but the other standout is the new first party themes available for purchase. They are very, very slick. Check them out: http://themes.getbootstrap.com