Most importantly, this has happened with a full month of sailing season ahead. A container ship leaving Europe today can easily make the transit into the Pacific. I assume at this point that we are using the narrow southerly routes to make the passage in the western part of he archipelago, but I suspect that even the western reaches of Lancaster Sound could be open in a couple of weeks.
Since the global climate appears slightly warmer, this new regime can become stable and will be reinforced by the substantial disappearance of permanent sea ice. We can expect that the annual sea ice for all the Arctic Ocean will almost disappear totally every summer once the permanent ice is gone. The sailing season will still be about thirty days and the Passage will still be the route of choice.
I do not know the precise transit times that will be achieved by shippers at this point. A lay over and a slow movement through narrow straits is likely necessary but could be built in as a matter of course. If Lancaster Sound is open, then an extra day or two could be saved.
In the meantime, the map distance is around 4000 kilometers from Shanghai to the Bering Straits. The Arctic leg is an additional 3500 kilometers to the mouth of Lancaster Sound or 500 less if it is open. The rest of the route to Rotterdam is another 4000 kilometers or so. This all suggests that the trip could be comfortably made in fifteen days. In fact with careful scheduling, it should be possible to complete a round trip for a one stop bulk transporter.
This will open the door for late season cruiseships between Vancouver- Seattle and Halifax – New York in either direction. Again it is easy to schedule around four weeks of safe passage time.