This isn’t a thought about trying for the sake of blind trial and error. If you see a guy has a good balance of attack and defence (comfortable going both ways), has good use of the football, then it would be a waste not to be tried there.Nothing wrong with pinch hitting guys around the ground for flexibility purposes. But we cant keep pinching players from other positions to fill midfield vacancies. Robbing Peter to pay Paul is not a winning strategy.
I can't remember Hart ever playing midfield which answers the question anyway. Id rather actually drafting mids than trying to convert players.
This isn’t to say it needs to be tried in a hurry, anytime in the foreseeable future would be ok.