Eh, I'm not left with just PS5/Scarlett cause the question wasn't time limited lol, it could be the generation after that or the one after that. Though even if I was just asking for PS5+Scarlett, it's more about the marketshare I'm interested in (% sold in Japan) than the 12m figure.
With each generation the % of total sales coming from Japan has declined for dedicate home consoles (27%, 23%, 14%, 9%, 7.5%) Will this number recover, that's the question, or are consoles that need hooking up to a TV to use dead for good.
One factor why the percentage has gone down is that sales outside of Japan have been growing in raw numbers. That's why improvement in raw numbers for Japanese sales would be easier to accomplish than growth in the share of global sales.
But in any case, let's go over every possible console manufacturer.
1. Nintendo is very, very unlikely to make another stationary home console because it will only lead to higher costs for them compared to what Switch is.
2. Sony had already relegated Japan to a tier 2 country at the time of the PS4 launch, hence February 2014 instead of November 2013. They've scaled back on Japanese first party efforts, they've introduced censorship policies and a more cumbersome process for Japanese third parties by forcing communication in English. The prospects for the PS5 aren't good in Japan and Sony has already shown that they'd rather move away than try to improve matters. The PS headquarters are in America today and their business decisions are clearly focused on non-Japanese markets. It's an attitude that fuels a cycle of perpetual decline in Japan, so placing any hopes on the PS6 would be wishful thinking.
3. Microsoft only does Xbox in Japan for the sake of presence, because no Xbox in Japan would mean as much as Microsoft doesn't give any damn about Japan and its developers. Said presence is enough to get Japanese games on the Xbox One, so there's no real incentive to invest more in the Japanese market than they do now.
4. Others - The reason why we haven't seen any company give a serious shot at a console since Microsoft's entry in 2001 is that the console market wasn't particularly profitable if you weren't Nintendo. It's only today that we see a company like Google trying to get a piece of the gaming market, but their approach targets the one thing that has been the saving grace for Sony's and Microsoft's efforts in console gaming: Subscriptions. That's the thing that has made gaming attractive for outside companies and nowadays it doesn't require the creation of a box anymore, so a new entrant in the console market can be pretty much ruled out.
The bottom line is that it's up to Sony and Microsoft to do what you've been getting at, and that's like wondering if either the Miami Dolphins or New York Jets will win a Super Bowl anytime soon. The only positive thing to say about Microsoft is that Xbox can't decline much further in Japan (XB1 is at 110k LTD). Sony is going to look to developing markets to grow PS sales, because that's going to be a lot easier than recovering in Japan. So those 12m (projected 13m) will see a decline to about 8m I would say and consequently another dip in the percentage of global sales that Japan accounts for.