In a recent blog posting, Herald journalist David Leask wrote: '[T]here are many places [...] where the concept of "foreign" comes with a sliding scale rather than a simple binary yes/no switch.'
However, is this only the case in some places? When we ask ourselves whether somebody is a foreigner (in the sense of "an outsider or interloper", not in the simpler sense of "a person from a foreign country"), don't we always arrange people and places on a sliding scale? For a person from Glasgow, I presume the scale might look a bit like this:
Everybody will have their own scale, depending on how familiar you are with other places. If you've got family in Norway and have spent most of your holidays in Poland, these places will feel less foreign to you than to those of your compatriots that aren't familiar with them.
Anyway, from a Scottish independence point of view, what's important here is that England won't suddenly jump from 1 to 10 on this scale after a Yes vote. If England is currently located around 4 and Ireland around 5, it would make sense for England gradually to shift towards 5, too, but it will most likely be a slow process, caused by an increasing unfamiliarity with the finer details of the other country's politics, TV, education, etc.
When Better Together warn that family members in England will become foreigners overnight after a Yes vote, it's clearly only true in the simplistic sense that they'll be citizens of another country; they won't feel more foreign at all.