For any new event, the need for a robust and efficient traffic management plan is essential. From my experience; I would say that any donor airfield needs to be no more than 5 miles from the major trunk roads, as in A Class duel carriageway or motorway. Ideally with a railhead nearby within walking distance. The access roads to the airfield need to be numerous to accomodate through traffic (people who arrive in taxis or dropped off by family) and also VIP/Blue light routing.
Leuchars operated a park & ride, and I cannot say how efficient it was.
Add to this a decent length runway and lots of hardstanding, and the shoping list starts to become claustrophobic. Many FJ require RHAG and/or Barrier to operate from and if not available; enlisting a second operating airfield becomes very expensive.
There are not many airfields in the north of england which tick all the boxes. Wittering could, but like Cottesmore, is not really far enough north to be RIAT(North). There will be no desire from any council to improve highways and byways for a once a year airshow. (Thinking of Leemng) Then when you go too far north, the footfall becomes insignificant. It is a difficult business case to satisfy and an easy one to let drop in 2017.