As absurd as it sounds, there may be a bit of method in your madness.
If the BBC put the News back to 9, then it would give them the opportunity to air something to grab the audience at 9.30pm which is too early for most peoples bedtimes at that point. Therefore a bigger audience to capture there who may be willing to watch later if there's something to capture the audience.
By 9.30pm ITV will likely be in the middle of an hour long drama which will prevent people from switching. ITV's news viewership will also likely dwindle given they are going to be an hour behind with the news, which these days offers no alternative than the BBC's offering.
However, I think the BBC would be more likely to shove their News to 11 rather than use up 30 mins of primetime. But it could be a useful tool to grab audiences for a little bit longer as currently 22.30 is the natural conclusion for most people to turn in to bed, you could easily maximise it to longer by removing that 'natural conclusion' after the news.
January 9th 1989 - December 3rd 2006