A lot of Western Europeans are concerned about allowing in the Bosnians and Albanians (let alone potentially the Kosovars and Montenegrins), even in the long term, because then the number of states in the EU will be heavily weighted towards the Balkans. Applying the 65% population key, this doesn't matter so much as their populations are pretty small. However they will definitely count towards the 55% of member states key. I see here an incentive, on European grounds, to recognise the independence of Scotland and other well-behaved Western European non-state regions, to try and rebalance the map a little more towards the West.
Hmm, I may have to flesh this out a bit. (or maybe not.) Thanks to feorag for reminding me of this conversation.