I'm glad they're supporting Bootstrap 3. The switch to Sass is unfortunate. I never had a problem with compile times and being able to pick and choose the bootstrap I needed in my own less build was really nice. I don't think I'll be using newer versions of Bootstrap. Once they stop supporting 3 I think I'll move on to a new CSS framework. I just think they shouldn't change builds like this on frameworks that are already widely used. I'm sure Sass developers were making use of Compass or other Sass frameworks if they needed to integrate the framework with their own builds.
I will never be able to understand why the grid class names are abbreviated. It's borderline unreadable and it's one of the primary reasons I avoid bootstrap when I can. Foundation is much better in this regard class="large-6 columns" makes much more sense than class="col-lg-6".<p>This is a good article though. I've been wondering what changed in the new version.
"It seems though that if you need Internet Explorer 8 support, you’ll have to stick to using Bootstrap 3."<p>I'm kind of surprised. No doubt some user bases have user bases running newer browsers, but with IE 8 still sitting at ~13% market share[1] I suspect this will prevent many people from using Bootstrap 4, including myself.<p>[1]: <a href="https://www.google.com/search?q=ie8+market+share" rel="nofollow">https://www.google.com/search?q=ie8+market+share</a>
Flexbox and Sass-first is a nice surprise, but the switch to rems steals my attention. I know that backwards-compatibility goals kept them on px, but that has long been my one complaint with Bootstrap (as a regular user, not as that guy who <i>"would use it except [minor reason]"</i>).