An increasingly ridiculous debate.
The EK 777 fleet will have Newcastle in the nav database, airfield plates readily available to the crews in whatever type of trip kit they carry, and all safety and handling audits completed for Newcastle as they fly there daily. Crew likely familiar with Newcastle and EK-trained ground staff in place at NCL to handle both an arrival and a departure. I very much doubt EK will maintain this currency for Prestwick where they might fly once in a blue moon.
That's even before you consider the weather that occasioned the diversion was so poor that road travel from PIK to GLA might well have been just as difficult as NCL to GLA - so distance becomes a disadvantage if the roads are decked with snow.
Unless an airline has cause to nominate an alternate and set it up as such to maintain all of the above capability for it to be used, then do not expect to see it being used as the #1 above another airport to which the same airline flies regularly. That goes for EK just as much as any other airline, and the mantra is true with increasing and direct proportion to the size of aircraft. Randomly electing to land a 777-300 into an airport to which you and your operator have never flown before is not a venture to be undertaken lightly, and certainly not at the drop of a pilot's hat when a no-risk alternative exists relatively close by.