With the PS5 approaching 5 million lifetime units in Japan, could it surpass the Nintendo Wii's almost 13 million units?

Unless Switch 2 is a flop, then...

The Wii sold 12.8m the PS4 sold 9.7m.

The PS5 is currently doing better than the PS4 in Japan. If the PS5 could keep up the current momentum it has in Japan then yes. This year is going to be the best sales for a PlayStation home console in Japan for 20 years. But I expect some sort of drop off.

It has a chance to beat the Wii but I'm going to say 10-11m.

But if I'm wrong and sales in Japan next year are almost as strong as this year then it'll beat the Wii.

PS4 couldn't crack 10 million, and PS3 sold 10.47 million. The ceiling for a PlayStation home console in Japan from PS3 onward seems to be around 11 million.
So of course, PS5 could outsell Wii's nearly 13 million, but it's unlikely.

Nah sales will probably be a lot lower next year. I think it'll likely reach 10m but it won't go much further than that.

Before this generation I expected 7-8m for the PS5, but this became very improbable quite early on already (read: 2021), because PS5 sales in Japan did not and still do not align with demand by Japanese gamers. Matching the PS4 became possible after a while and now with 2023 being almost over, anything under 10m is unrealistic.

I don't rule out that the PS5 could surpass Wii sales, because the exports of PS5s sold in Japan might continue for another couple of years or perhaps even longer. Predicting PS5 sales in Japan isn't straight-forward because of this big X-factor.

PS5 most likely will have a longer lifespan than the PS4. Let's say it has 8 year lifespan then it needs to AVG 1.5m a year and then another million after the PS6 releases to surpass the Wii which I think is possible

Lets take a look at past PS consoles to get an idea how well PS is received in Japan.
PS5 is at 4.75M.
PS4 sold at 9.66M
PS3 sold at 10.47M.
PS2 sold at 23.18M.
PS1 sold at 21.59M.

Now I want to look at the percentage of each (comes from # sold in Japan/# sold worldwide).
PS5: 9.71%
PS4: 8.24%
PS3: 11.98%
PS2: 14.61%
PS1: 21.06%

Since Sony's direction to apply Western ideals, they have lost the appeal of their home country. The PS5 is in it's 4th year of selling, and the PS6 is rumor for 2027 (could be pushed to 2028). PS5 has about (Im gonna go with the later year for a basis of the maximum) 5 years. This year so far the PS5 has sold ~2.3M. If we assume PS5 will sell at least this well for the next 4 years thats an increase of 9.2M. But the PS5 won't be able to do forever, there is always a peak year and slowly decreases in sales. Let's say in in 2 years is the peak, and after it's peak year it sells -10% to 20% (based on Switch after peak years) compared to the year before. And PS4 is still selling, and probably will for another year, so lets say PS5 will sell 5 years into PS6 life. But once PS6 releases the drop will be -20% to -30% of a drop (maybe more).

I think the PS5 worldwide will sell 124M

Ok, so we have an idea. Loose idea, but an idea.

PS5 is at 4.75M + 2.3M (2024) + 2.3M (2025) + 2.07M (2026) + 1.86M (2027) + 1.49M (2028 PS6 releases) + 1.19M (2029) + 0.95M (2030) + 0.76M (2031) + 0.61M (2032) + 0.49M (2033 sold out) = 18.77M

18.77/124 = 15.13%
18.77M will be it's maximum if all goes well. If PS5 has already reached it's peak then it will reach 13.01M. 10.49%

Yes, PS5 will surpass the Wii (12.77M) just barely but it will. Do I want it to no, but I'm trying to be realistic.

I'm just not as optimistic as some of you folks.

I will concede that the PS5 will probably pass the PS4 due to the high export rate, which is something I've said formerly was highly unlikely, but never impossible.  And I'm the first to admit that I'm not great at predicting exactly where Sony's hardware will end up.  For example, I initially thought the PS4 would sell less than 110m.  I was wrong about that.  Then, later on, I thought it would sell over 120m.  I was wrong about that too.  And I do think that PS5 is poised for huge numbers world-wide since Xbox seems to be incapable of impeding its progress and Switch 2 will co-exist without holding PS5 sales back.

But with the conscious choice to make the Playstation 5 a very western-oriented machine, it's not really what Japan is fond of, and as a result, I think PS5 sales are going to drop tremendously in the region once Switch 2 arrives simply because almost everything will be coming to it.  Playstation systems have been able to rely on a number of 3rd party games not coming to Nintendo's system due to the power gulf but I think Switch 2 is going to be so much closer and able to get the vast majority of 3rd party games on board, that people are going to choose form factor over better versions of games in droves since  Japan cares about that much more and Switch 2 will be good enough for most people when it comes to the next Monster Hunter.

Except for Dragon Quest and Monster Hunter World, what does Playstation have left in the future that Japan really cares about?  And I believe that at least one of those 2 will be on Switch 2 as well.  So, even accounting for all of the exports I can only entertain the PS5 crossing the 10m mark in Japan at some point, and even then, not by much in my opinion.  And there's a pretty large gap between 10m+ and almost 13m.

Possibly, yes. The Wii was never really that big of a hit in Japan.