Iceland does seem a bit of a stretch, though time will tell... Yeah, but it's more a matter whether the US wants to invest in taking it during a time of chaos. The Danes may try to fight back...but they're too close to the Liberal War Northern Theatre to be able to project power far from home without risking a lot more than Greenland. Her allies are out of position to help that far to the Northwest. And British interests are not optimal for the Danes to count on their intervention. You might be surprised.... A real filibuster attempt at Iceland would probably fail, yes. Then again, so did the attempted filibusters of OTL. The only Great Power that the US really has to fear is Great Britain - other powers would have to go through the UK to get to the Americans. Without at least tacit permission from the UK, any Great Power would be looking at a war far from their supply lines and against both the US and the Royal Navy.