If you’re assuming that the Scots courts currently permit retrials following a ‘not proven’ verdict, then you assume wrongly. The same ‘double jeopardy’ rules apply as with ‘not guilty’ verdicts. Indeed, the ‘not proven’ verdict survives (apart from sentimental reasons) mainly because the accused cannot be retried. It allows the jury to cast doubt on the accused’s innocence in the knowledge that he/she will never be convicted on the particular charges before the court.
I don’t really see why you think there would be anything to gain from the introduction of ‘not proven’ verdicts elsewhere. There is an argument for saying that the emergence of important new evidence should allow retrials, but the whole point of that argument is that the original jury was not in a position to consider the full facts. If you want retrials, you surely believe that it is the case presented at the second trial, not what the previous jury thought, which should matter.
You should also not assume that there is much support for the ‘not proven’ verdict in Scotland. Many, including prominent lawyers and politicians, want to see it abolished. I would support abolition. It is however one of those issues which is never a pressing political priority, not least because the verdict is one which is used only very rarely.