Too many factors that would affect the outcomes of all the promised flights, but it's always prudent to have your bases covered in advance, and if things don't pan out, then there's only the fees of the landing slots etc to lose.
As to the China Southern flights, perhaps they have enough capacity already on their A380 flight and the other rotations already ? There won't be much passenger traffic between the UK and China at the moment, so it's all about cargo.