This is what I meant earlier when I said I was more of a qualitative analysis person. To me, the relevant bandings are as follows:
30-32 Million:
-DS
20-22 Million:
-3DS, PS2, PSP
10-12 Million:
-Wii, PS3
3-5 Million:
-Vita, Wii U
What matters to me is the trend these systems are fitting into. If you look at the list of recent platforms, each generation we see successor platforms dropping one or more tiers in terms of their sales potential.
This is a very unhealthy trend for dedicated devices. If the PS4 ends up at 6-8 million units and/or the NX ends up at 14-16 million units, that's worse yet. Even if they're only dropping half a tier, we're continuing to see a strong erosion of what remains of the dedicated industry.
Did the Wii end up marginally ahead of the PS3? Sure, but I'm not sure what meaningful takeaways there are from that.
Yes. Japan is no longer a relevant dedicated market on the global scale, so I doubt they will focus on the market beyond providing promotional and technical support for any Japanese developers who want to work on their platform, and a couple of token games that will overwhelmingly consist of titles that have notable appeal in the West as well.
Sony already works with a lot of regions where they don't sell much (see emerging markets), so they can ultimately treat the region the same way they would for a large emerging market that can't sustain heavy first party support for local tastes. It's up to Japanese third party publishers if they want to continue on making games for the platform in an effort to sell more in the West despite a poor installed base at home.