Holy crap. So Switch is already on track to surpass PS4's 2018, I really didn't expect the Lite to have such an impressive second week hold. If this keeps up, 20 million should be a pretty easy target.
I agree that Switch will sell more than PS4's 2018 this year, but what do you mean by already on track?
Week 39 has Switch at 9.25m vs 10.3m for PS4's 2018.
18.8m has been by prediction for a while, it has a good chance of surpassing that I think, but I don't see it reaching 20m.
Already on track because Switch 2019 has outsold the 2018 numbers week after week, and if you look at the total end of year 2018 Switch numbers and add the margin that Switch 2019 has already built up on it, it's more than the PS4 2018 numbers. It's unlikely to suddenly start selling worse than last year after doing so well so far, so I consider it to be on track for 18.3 million right now, with a possibility to build on that significantly.