I think the other points made by Flightrider are fairly accurate and probably reflect the thinking of most on here. However I would think it likely that EDI-SOU was just an indicative regional route for the news media - after that comment was made, easyJet have of course set up a (minimal) presence at SOU which may indeed deter any new operators on such routes although I would think otherwise.
The hydrogen powered Twin Otters are still slated for 2025 according to
this press release but I don't see how they will be able to viably compete with Loganair on a network within Scotland, which one presumes is the intention with an EDI base.