I remember some time back in possibly 2009 Alaistair Stewart and Steve Scott did an evening news bulletin together. It just didn't feel natural at all.
Chris Ship did a lecture or speech some time afterwards at Leeds University and he did make a reference to it, there was a video of this floating around somewhere not sure if it was on YouTube.
I do recall that it had occurred because of a scheduling/rota mix up, and looked rather strange for two male anchors to be presenting the 6.30 bulletin, I don't think they would probably do it intentionally again, but I suppose it depends on the anchors and there chemistry.
Both Nina and Katie Derham anchored a lunchtime news bulletin a few years ago and it felt very strange for Nina to be the lead presenter, but I can imagine Mary/Natasha Mary/Julie Natasha/Julie presenting lineup working very well.
I can't see Mark and Alaistair line up working very comfortable on air unless it was a special bulletin because of breaking news or an Election Special.
Totally Random news