The "jurors kept in the same hotel as witnesses" could be an area the HCA wants to make a precedent on, the same reason leave to appeal was granted by the VCA. Even though it seemed unlikely that the way it played out could have resulted in a tainted jury (which is why the VCA rightly dismissed the appeal after granting leave), I could see a desire to set some boundaries to stop it happening again.

I forget the details of the mobile phone data evidence, but again, given the VCA decided to grant leave, it seems a potentially novel area of law that the HCA may want to set some rules around.

Those would be the only reason I could see the HCA taking the case.