What does non-US mean? European Founders could register a Delaware company. Is that good enough?

Partially. By investing in a delaware corp they know the law that will apply, and the tax code.

However if you're far away it's harder to keep up with what's going on with your company and many will not want to deal with that.

How much harder is it for an SFBA investor to keep up with what's going on in a Berlin or London startup vs, say, an Atlanta or Miami startup? As long as you need to board a flight to get there isn't it more or less the same, whether that's a 4 hours flight or an 8 hour flight?