With regards to year round ice free, I still have a very hard time trying to understand what would prevent ice forming in the long, relatively cold winter night any time soon. Would it look like today's ice? No. Will some form of ice form on large sections of the Arctic Ocean and peripheral sees? How could it not?
Ocean currents could play a large part in any year-round ice free Arctic. As an example, it's cold enough at the moment for large areas to freeze over in the Chukchi sea at 70N. On the other side of the Pole, the north Atlantic is not freezing at 70N and hasn't for thousands of years. This year there is even a year-round patch of open ocean reaching to 80N north of Svalbard. Not only is it not freezing over but actually melting the steady stream of ice that moves into it from the north.
An ice-free Arctic in summer could change ocean dynamics sufficiently so that the seas will have a very hard time refreezing. Long-fetch waves could stir up warmth from below, and the warm currents might extend their reach further north.
Ice would presumably still form along the coasts and in sheltered areas, but an open Arctic may become too dynamic for refreeze, and higher ocean temperatures could keep air temperatures above the -11 or so needed for the ocean surface to freeze.
I think this is not an unlikely scenario, and it's the only mechanism I can see that could cause a year-round ice free arctic within the next century or more.