Twitter is social-networking web application, and twitter-bootstrap is a popular development framework originated from twitter for creating web application front-ends (including web GIS). In my opinion, these two are quite different. Twitter-bootstrap as a technology is often used in applications that has completely nothing to do with twitter or social networks.As a GIS example, OpenLayer's dev website has an example for ["bootstrapped openlayers"][1].
I my opinion, it would be mistaken to use the same twitter tag on questions about e.g. the twitter social network data and questions regarding how to use twitter-bootstrap to build a web GIS (the technology).
Also, I wish to add that Bootstrap-3 is not backwards compatible with previous version. There has been a lot of discussion on SO of migration issues from Bootstrap 2 to Bootstrap 3. We may or may not be able to cover all bootstrap questions with one twitter-bootstrap tag, depending on how much questions are concerned with one version vs the other.
So I think yes, there is a need. I actually was asking (the one question mentioned in the OP) about issues with using bootstrap-3 to create a web GIS. And it would be misleading to tag such as a twitter question.