Top 10 consoles in Japan (taken from VGC):
1. DS - 33.01m
2. GB/C - 32.47m
3. 3DS - 24.59m
4. PS2 - 23.18m
5. PS1 - 21.59m
6. PSP - 20.01m
7. NES - 19.35m
8. SNES - 17.17m
9. GBA - 16.96m
10. Switch - 12.81m
2020 did not provide much opportunity for Switch to move up in the rankings. Only the Wii was a realistic target and that has been passed already. The rest of this year is merely about getting into a good position to overtake a few consoles in 2021. If Switch manages 5m in 2020, its LTD will be 16.4m, so not far behind the GBA's lifetime sales anymore.
I have had a high confidence level that Switch will finish as the third best-selling console of all time in Japan because I was aware of the 3DS's sales curve and how an early deficit for Switch wouldn't be something to worry about. The past two weeks certainly didn't make me less confident, so the next-best target - beating 3DS and Wii U combined at ~28.0m because they are Switch's predecessors - is also looking more realistic now.
Switch has passed 13m this week (this has yet to be reflected on VGC's platform page) and it's still far away from reaching its saturation point. Properly supported home consoles land at ~20m in Japan while portable consoles have a higher ceiling due to individual ownership rather than household ownership. Switch can take advantage of both, so ~20m hybrids and ~10m Lites lifetime isn't that much of a long shot. Currently, the hybrid SKU is at 11m LTD and the Lite at 2m LTD. Of course Nintendo has the option to do a refresh for both SKUs akin to the New 3DS to reinvigorate interest in the latter half of Switch's lifecycle, so fall 2021 or later; likewise, they could come up with a third SKU if they think that makes sense.
And if Nintendo is serious about giving Switch a long lifecycle and stick with it in a highly committed manner, then even the #1 spot is in the cards. Switch would need more years than the DS to reach a total of 33m, but it can get there. After all, Sony has voluntarily ceded more and more of the Japanese console market to Nintendo.