TCL, I don't dispute what the Law Society of Scotland says, but I do dispute your understanding of it!
Indeed, the Law Society of Scotland has suggested that it might be contrary to EU law if Westminster attempted to deprive anyone of British citizenship merely because they had acquired citizenship of another member state ie Scotland.
So the process would be this:
Scotland votes for independence
A given Scot is then a Scot and not an rBrit
Said Scot then applies to rUK to be an rBrit
If said Scot qualifies to be an rBrit they are granted rBrit nationality.
rUK may not deny citizenship on the basis of said Scot being Scottish, but may OF COURSE deny citizenship on other grounds, e.g. said Scot was not born in rUK, did not have rUK parentage and did not live in the rUK.
Really, what do you expect? Independence AND ongoing nationality of the rUK. You have got to be joking!
The "transitional arrangements" would be to sort out en masse situations like you would find in Corby, where loads of people would qualify for dual nationality. That's fair enough.