A customer has bought a SuiteCloud+ licence and people are making noises about scripts being updated based on this change. Is this just a case of going through and working out the script priority? (I have it in mind NS dictates the queue a script ends up on these days).

That's correct, you can no longer specify the script queue, although, if the script was deployed before queues were deprecated, it will still respect the original queue assignment. Yes, you will need to determine which scripts will receive an elevated priority. See SuiteAnswer 10638. You do also have some settings to configure in Setup>Company>SuiteCloud Processors