At the time of the Scottish independence referendum in 2014, I remember there being warnings from the EU that rejoining would not be a simple matter of just applying for an independent Scotland.

I could try to find some links on that if you like, but the way I remember it is that the EU was against the idea of Scotland going it alone and EU officials actively worked to discourage any ideas that an independent Scottland would be received with open arms.

But of course, that was before Brexit and while the UK was still an EU member whose national interests were taken into consideration by other members (because EU). This is not the case now.

Still from memory -sorry for that- but when the last UK MEPs were making their parting speeches at the EU Parliament, one Scottish MEP finished his with an impassioned plea to the EU to not forget Scotland. Which I interpreted as a plea to make it easier for Scotland to join the EU if it ever gained independence from the UK.

The EU was against Scotland unilaterally declaring independence from the UK, because you know, Spain/Catalunya, Romania/Szeklerland, Italy/Veneto, Belgium/Flanders,... (the list is endless).

But otherwise, Scotland was part of a former EU member, I imagine they would not necessarily use the pound (a Scottish pound would probably be weak), so they'd probably adopt the euro in a short while, there is a ton of cultural affinity with the EU, probably more than for England in some regards, etc.

Scotland for sure could get an accelerated membership process if they do decide to become independent. They could even start some of the paperwork or at least contacts before they gain the official independence, I imagine.

The EU would for sure accept the membership request. They'd probably accelerate it, even.

Before Brexit the only blocker was a unilateral declaration of independence, which will not happen. Scottish independence will most likely be a mutual separation.

And after that the Scottish budget will be hammered hard so I imagine they'd definitely want to join the EU ASAP to get help. Access to huge markets for exports, cheaper imports, EU funding for developing regions, etc.

Currency is one of these aspects that are the least problematic here (many EU countries have their own currencies, and it was the same with the UK). What is more challenging is that becoming an independent country takes time, and if it happens, Scots will have their own challenges. Joining the EU will definitely possible, but I can't imagine it would be a quick process. Whereas if the UK changed their minds and decided to rejoin the EU, you could expect it could happen within 3 years or so.

It would be very popular move for every EU politician to fast track Scotland to EU. But yes, it would be complicated to separate from UK and become independent. Becoming EU member would not be that complicated.

Spain and France aren't super keen on encouraging the general idea that regions of a country can easily split off and become independent EU member countries.

Spain I understand. But I dunno about France. It's not the Auld Alliance is still a thing, but surely they'd relish an opportunity to give England a black eye.

Being French I can tell you we really discourage it because we don’t have just one region but several! You have Corsica who wants to be independent, Alsace who wants to be independent or linked to Germany and sometimes Basque linked with the Basque region of Spain.

But all that was at its apex years ago now it’s more stable.

There's also French Catalunya, of course.

But Scotland is already a country.

That is the nomenclature in the United Kingdom, but outside we don't consider Scotland England, Wales or Northern Ireland to be countries. They are part of the United Kingdom, which is "the country" for our purposes.

Ever heard of that thing called the "Basque <<Country>>", for example? :-)

In England we have "the Black Country"[1][2] but it's not a country or a nation (or anything to do with race or skin colour) or even a clearly defined area, but a region of early industrial pollution and coal mining. We also have "the West Country"[3] which has its own sea borders, regional dialect, Cornish language, but isn't a nation or a country.

And we have "God's Own Country"[4] which is a phrase but does have an independence movement[5], and a region (Mercia) which hasn't been a place since 527-897CE but still has an independence movement[6].

[1] https://en.wikipedia.org/wiki/Black_Country

[2] https://bclm.com/

[3] https://en.wikipedia.org/wiki/West_Country

[4] https://en.wikipedia.org/wiki/God's_Own_Country#Yorkshire

[5] https://i-yorkshire.com/yorkshire-independence/

[6] https://independentmercia.org/declaration-of-independence/

A country is a sovereign nation. Scotland is a nation, but it does not have full sovereignty and is not recognized as a sovereign nation by any other sovereign nations (to my knowledge), the same way that Catalan is a nation within the country of Spain.

I thought the problem was that Spain wouldn’t like it because that would set a precedent of rewarding independence movements they oppose like for the Basque region?

Not necessarily if the separation is agreed upon by the UK central government: Madrid's main problem is a unilateral declaration of independence.

WRT currency having Scotland use Euro wouldnt be any different to how Northern Ireland uses Pounds and the Republic uses Euro

It is all complicated, but have you had a look lately how complicated brexit is? So I'd say we're at the point where it's about picking which kinds of complications you prefer.