Scap is the deployment tool used for production cluster deploys and one of the goals of beta is to track production as closely as is reasonable (bug 51494). Using scap to push MediaWiki updates across the beta cluster will provide a good test of changes to the scap codebase. It may also improve the speed of the wikis in beta slightly by allowing them to use local storage rather than NFS for l10n cache and the MediaWiki php code.
There was a previous effort for this documented in bug 37078 which was WONTFIXED a year ago. At that time git-deploy (nee trebuchet) was slated as the replacement. Although git-deploy was configured (see bug 43339) at some point this was abandoned and shared disk became the method of deployment again.