Whichever way you look at it, there are no winners from the adopted position on the currency union.
Despite the fact that there are a number of factors that are making the currency market jittery with Sterling (and I don't think the YouGov poll has realistically contributed that much to it at all) then there can only be a bad outcome for rUK, and to an extent Scotland. Outcome is that it weakens the £ through market perception/uncertainty then this is not good. If they refuse a CU then we walk away from debt and added to that the rUK takes a hit on Balance of Payments and loses approx. 9% revenue = not good. Despite the fact that we can use the £ regardless then this wouldn't be good for us to operate with a weakened currency against the euro, yen, dollar, etc. If we were to then decide to launch a Scots currency due to a weakened £ then this would be difficult as well as we'd be wanting to peg it to the pound to ensure stability of Scottish/rUK cross border trade and also have the transactions costs coming into play.
The more you look at it, the more ridiculous it seems that Westminster have put themselves in this position for political posturing. I'd expect a rapid turnaround on this issue after the vote before it even gets to the negotiating table - although in reality it will probably be dressed up in a manner to save face for the Westminster Gov.