I have to agree with you on the point of Brexit in so much as Scotland voted to remain, therefore personally do not see why Scotland should have the choice to remain as part of the UK.
I don't believe Scotland should leave the UK and think it's tantamount to economic suicide for them to do so as long as they aren't guaranteed a place in the EU.
Might just be me but I cannot foresee any circumstances in which Spain would allow Scotland into the EU and the vote has to be unanimous. It would require either a change of legislation, a change of the political landscape in Spain/Belgium/couple of other countries or a change in mindset.
What we're seeing at the moment is a descent of Europe into nationalism. British nationalism, Scottish nationalism, Flemish, Transylvanian affecting both Hungary and Romania, and of course Catalonian and Venetian nationalism. Many of the major countries in the EU are going to have huge problems with secessionist movements over the coming few years due, in part, to the Scottish nationalist vote and many of them have a strong political will to keep them down.
Just as the Kings of Europe once colluded to keep down the will of the people and retain their monarchies, the major countries will do so again in order to keep their administrative districts as large and collective as possible.
We've been here before when Europe descended into nationalism and it didn't work out very well for all concerned then either. You have to imagine that AT LEAST Spain and Italy will really have a problem with allowing a secessionist Government into the EU, let alone the problems in the Baltic region or Northern Europe/the Netherlands.
It's not too much of a stretch to suggest that the EU could well look like the
Holy Roman Empire again before too long if these nationalist movements continue to be embraced.