I'd normally criticise schemes such as this, but I think there's room for a couple of routes driven by N Fife/Dundee demand, plus the obvious inbound attraction. I wouldn't see it as an alternative to EDI for FR though, I can't imagine many pax heading to Edinburgh itself would want to travel to Leuchars when they can fly to EDI with other airlines, even if FR were offering giveaway fares.
I'm not sure any of the logistical issues are insurmountable tbh, I think they could all be sorted. The problem is there's no terminal and the only way you're going to get one is public funding - I can't see any such funding being forthcoming and complaints from GIP EDI would be vociferous to say the least. Given the EU aid rules mentioned earlier aim to prevent the development of excess airport capacity through state subsidy, they could cause trouble too.
At the end of the day, this comes up every 6 months or so and it will probably never amount to anything.