Recenti weeks were more positive but until few weeks ago trajectories pointed at a possible ltd around half of the ps3 one so more or less 5 millions. Aldo accounting your numbers that would put PS4 around 2 millions after two years on the market with two christmas and the launch, and looking at a shorter lifetime before ps5 introduction I would say that your and his calls are closer than you think
What's most interesting to me is that the PlayStation, the new console on the block, in a market dominated by Nintendo and Sega, was able to sell through more than 2.7 million units in the same time it has taken the PlayStation 4 to sell through 1.7 million.
Even the PlayStation 3 which launched at a much higher price had already sold through more than 2.1 million units when you align launches and consider how much better the Nintendo Wii was selling.
PlayStation 4 software sales have been very low as well with no games apart from Bloodborne and Dragon Quest Heroes able to exceed 200,000 units with the latter game selling more on PlayStation 3.
There hasn't been a killer app yet for Japanese gamers to purchase the PlayStation 4 and honestly the market has changed so much that even if killer apps do launch it may not do much to increase the install base to the levels of its predecessors.
The launch of PlayStation 4 exclusive titles from Sony Computer Entertainment, Square Enix, Capcom, Bandai Namco and Koei Tecmo in 2016 and beyond will be key to pushing both software and hardware sales as right now there don't seem to be many other big developers catering to the Japanese market that have the strength to dictate hardware purchases.