DBS are doing the entire Chiltern RHTT programme this year, including the Met between Great Missenden and Neasden. (Last year they did everything except the Met, which was covered by the Chiltern Railways "green goddess"). Apparently some 66s have been fitted with tripcocks for this work.
As far as I can ascertain the "green goddess" is going to be on standby as a back up in case of failure or if additional trips are needed.
It seems unlikely that the maroon bubble will see any use this year.