An administration wanting to become independent is not the same as a country voting for it. Though it is odd to single out Sturgeon, as you and mreckless have done. It's not for me to speculate as to why you've focused your comments on the leader of a party that is basically bossing politics north of the border and has been for a while now. She is simply the current leader of a movement that had legs before she took over and which clearly has significant support amongst the population of Scotland now.
In any event, the point is that Brexit will be the final cause. Independence does not happen from nowhere or from one cause. In Scotland's case Brexit has crystallised an argument the SNP were making and more people appear to now support leaving the Union, though of course only time will tell.
Your comment about Wales makes little sense in either the context of the history of Welsh independence or in relation to Scotland. Not least because at present Plaid have not really built up a head of steam as far as independence goes - I think they are making more of a success of being a centre-leftish party in opposition to Labour than they are of persuading Wales it wants to bin England. If the Union crumbles post-Brexit that might change. It might not, but it's not inconceivable, is it?
NI was plodding along under the GFA. It may or may not have managed to carry on once they'd resolved the Stormont nonsense, but that ship has sailed now. Or at the very least is at the harbour wall waiting for Brexit to blow it into stormy waters. You are right about the tragedy of religious bigotry and its role in NI's history. I have little time for either side in that regard. Regardless, Brexit will be the catalyst for NI leaving the UK. What will follow over there may well not be pretty.