A Scandinavian megacity?

[The Oslo to Copenhagen] corridor is the most densely populated stretch of Scandinavia, home to 8 million of the region's 20 million people. An ambitious plan aims to link up its cities, medium-sized by global standards, across three different countries to form a single megalopolis - '8 Million City'.
The glue that will hold this megacity together? A high-speed train link that should reduce rail travel time between Oslo and Copenhagen from 7.5 hours today to 2.5 hours by 2025.

More at Big Think, which notes that expansion with a side link to Stockholm would create a 12-million-person megalopolis.  Personally, I would argue with the hypothesis that "next-level development is hampered by the demographic dispersal in small, relatively isolated urban centers," but obviously there's big money at stake here.