I have serious doubts about Glasgow as a visitors destination to maintain a route like SFO.
What numbers are you basing this on? Many inbound US visitors tend to do the Highlands as well as Glasgow and Edinburgh. Hence they can happily use GLA or EDI. As for Scottish people going on holiday, for two weeks in the sun, the additional trek down the M8 isn't a huge issue. Given it's Point to Point with Norewegian, it's not going to be massively business focussed and not time critical. GLA has more than seven contact gates that can take long haul on a dedicated pier. It's a much better passenger experience in my view, though getting worse as it gets properly busyt again.
It's not THAT different a world in Edinburgh, I've lived in both. Now Cumbria, that's a proper different world, mainly sheep
