When this mention of a Northern (and I think we should stress Northern not just North East...) Showbus-type event first came up, I offered the expectation that it would have to be somewhere central to all areas of the north. To me that means somewhere in Yorkshire would be likely to attract the highest number of attendees from all surrounding areas. I don't think the travelling would be an issue, after all look at where the attendees of the current Showbus travel from. As to where exactly an event of a large size could be held, I think you would be looking at somewhere like Elvington or Church Fenton near York.