There's some talk that countries such as Spain might not be too welcoming of a new devolved country entering the EU considering their own issues with the Basques and the Catalans. If Scotland devolved then there may be a push for devolved government and/or full independence from both regions.

Many of the SNP plans rely on the rest of the UK and other countries playing fair but there's no guarantees that England, Wales and Northern Ireland would allow Scotland to continue to use Sterling as their currency. There are a few UK military bases up in Scotland and there are no guarantees that they'd remain either. North Sea fishing and mineral rights may not simply start at Berwick and negotiations for both could go on for years.

Then throw in potential issues with areas in Scotland like the Shetland Isles who may want their own independence from an independent Scotland.

The SNP seems to have looked at all the good bits of an independent Scotland whilst ignoring the potential bad bits. It could become a real mess.