Obviously there is no actual precedent yet for this but as pointed out in Snubles post, the licence is valid for any multi engine aircraft as a co pilot provided they have a rating for that aircraft type. It would seem illogical to rate a pilot for one type of aircraft and that's all he can fly for the rest of his working life. I see nothing in the legislation that states the MPL Pilot would need any other training than passing a type rating.
The only disadvantage the Stirling Pilots would have against their CPL/IR/ TRTO trained compatriots is that they do not have the option to go and fly in a single pilot aircraft.
I feel also that the title to David Learmonts article in Flight International "MPL Pilots on the Scrapheap" or words to that effect, is hugely misleading. FTN got it right with "MPL Pilots laid off"