I am in favor of the trend toward dissolution of traditional nation-states in the EU in favor of greater regionalism. This is in line with the
principle of subsidiarity. If the end-game for the EU is true union, this makes a lot of sense, as eventually nation-states would be a more artificial structure that would stand in the way of this principle. Breaking up nation-states into more regional and identity-based political structures is a good way to pave the way for a better union.
Unlike the US, Europe's multiculturalism is far more geographically based. If a Europe of regions emerges, local identities may yet flourish under the EU. As things stand, we still have some cultures and languages under threat from centralized majority thinking.
Don't know much about the Scottish case, but I totally support Catalan independence. Apart from the foregoing, Catalonia basically is fully integrated culturally into modernity, while most of the rest of Spain remains mired in tradition and authority for guidance. An independent Catalonia would be a much more dynamic and productive member of the EU without all the gaming done by the central govt to hamper its performance.
OTOH, most member states are flat against this idea, and adamantly oppose it, with Madrid being the most obviously retrograde in its ideas about self determination.
And GB is clearly far removed from any sort of political union, hoping to retain a mere common market for goods. Too bad GB has totally forgotten all the problems with the 'snake in the tunnel' approach to exchange rates that system had as a "feature," and which made the euro necessary, which in turn makes political union more necessary. Either compete totally or integrate; half measures have no stable equilibrium.
It is either full steam ahead or scrap the whole EU. But the former was seriously placed in threat by the overly hasty incorporation of the wildly differing economies in places such as southeast Europe, making integration far harder than it would have been with 10-12 core member states.