I remember contributing to a Code for America project and the guy who was organizing it really wanted to use Bootstrap 4. I objected and noted that, for one, Bootstrap 4 is an alpha-stage project and there is very little reason to use it for a new CfA project. That it will break during development cycles, be harder for new developers to pick up, and would make it harder to target Microsoft (read: Internet Explorer) driven machines used by government employees.

His response was 'nawh.'

That was... a year ago, I think? I stopped contributing for other reasons but it's somewhat humorous that Bootstrap 4 is still in alpha.