I don't condone the idea of one locomotive being repsonsible for the sacrifice of others, regardless of how iconic that loco may be. However, privately owned locos of all types are overhauled and maintained to mainline standards relatively often, and whilst it is recognised as being hugely costly, it is clearly something which can be achieved by the right people. Indeed, to bring Tornado back into the argument, if that group can manage the ultimate achievement through their efforts, there has to be scope for anybody with a loco which already exists! If locos which are less 'famous' than 4472 can go mainline and not send their owners bankrupt, then I see no reason why Soctsman should cause major issues for the NRM or anybody else. If the financial backing isn't currently there, then there is the option of seeking other backing, or allowing somebody else to take on the task, or indeed just waiting until the time is right. If the cost to the NRM is such that an entrance fee would be needed just to pay for Scotsman then clearly it is the wrong project at the wrong time.
If it can be managed properly, at a reasonable cost, then a project to keep 4472 mainline and paying it's way is surely preferable to having it stuck in a building somewhere doing nothing other than gathering dust. Indeed, why preserve anything if all we wish to do is stand and look; a photograph is a good deal cheaper. Both enthusiasts and the general public clearly appreciate the idea of a 'steam train' working as it was built to do, hence the many heritage lines that we are fortunate enough to have in this country. To clarify my previous thoughts, I am not suggesting that the value of an asset like Scotsman should be hiked to stupid levels which cause the enthusiast fraternity to struggle with it's upkeep, merely that if it can remain a profitable asset to whoever owns it then that is a good thing.
Having said all that of course, if there simply isn't anybody out there willing to pay, then static exhibition status is all that remains.