@ggam while working on this pull request, I noticed the core teams intentions seem / looks like they are planning to make .alert class behave like .alert-warning (by default) (just my assumption), which I think will not be good idea, it will be good if .alert is used like .btn class is being used, so if we apply special class it delivers meaning to it like (.alert-success etc) by default it should not reflect any state (in my assumption .alert-warning), if user wants warning alert he / she should explicitly mention it.

Hope it answers your qeustion.