"The suggestion that some other anthem would be welcomed by nationalists in Scotland, Wales and Northern Ireland just doesn't make sense"

That is absolutely true! If someone dislikes the idea of an anthem solely because it represents a union they wish to sever - then it doesn't matter which song is used. Plus I think as far as Scotland goes many people mix up the idea of Scottish Nationalism and Republicanism. Of the two biggest political parties here the SNP have republicans in their midst but so do Labour! The SNP however are not a Republican party. On independence the Queen would remain Queen in Scotland. The plain fact is that many Scots had issues with GSTQ before the SNP became the major force they are now. Nationalism is only one of the reasons why many Scots don't feel close to this song.