@darius my understanding is that the purpose of Boostrap is to move the core infrastructure from uicommons (which is OpenMRS maintained) to a more widely used toolkit that web developers from other walks of life can help and for the dev team to focus less on keeping the low level plumbing maintaining css/html.
Now that Ref App is looking to add configurable dashboards as well as widgets for the Patient and Clinician facing dashboards, with React/Angular and other UI frameworks, there needs to be a standard to what the well formed HTML will look like, so there will be more non-OpenMRS relevant widgets.