Unfortunately, it doesn't seem likely to happen as 3 pages have stated. However, I would like for the Great Central Railway to bring back the Mail train runs at some point, as it's another attraction on the railway in its own right, and such an experience is hard to replicate, as there are no more mail trains.
Then again, the same could be argued for water troughs, and I doubt they would be reinstalled on that line any time soon .
What I would rather is to have more protection's for frequent mainline steam routes such as the West Highlands 'Jacobite' and Settle and Carlisle routes for steam, having window slots so that you can hear the locos, and ways to make the routes a bit more affordable, whether that be discount codes from the railcard site offer or a HRA card.