Joomla Production team have included it Joomla 3.0. This will provide a common CSS and markup to be used by developers.
We have also heard that they have names it JooStrap – combination of Twitter Bootstrap and gantry framework.
Following was the words from the team Member
"I envision Bootstrap to be the cornerstone for the JUI, which is a centralized, core "SDK" for components with minimal styling and consistent, standardized HTML markup that can be a starting point for any component, frontend or backend output."
This will make the styling of the site very easy.