Switch will have had a massive head start on the other two consoles.. And because it has a firm grip on Japan and is very strong in America and UK as well, by that merit alone it's highly doubtful that XB will even get close surpassing it. The only time a MS console has surpassed a Nintendo one thus far is the original Xbox (well and Wii U if you count that) and this was largely because of how much Nintendo dropped the ball with those consoles, and even then it barely edged it out Cube by a couple million. And I like the Xbox line of consoles, but there is nothing to indicate to me that MS is capable of selling more hardware than Nintendo.
Sony is more of a question mark. Their next console certainly eventually can pass the Switch, but it'll take a long long time to do so, and who's to say the Switch won't have long legs? I tend to think it will, as it seems to be trending more similarly to a Nintendo handheld than home console, like the DS/Gameboy, which makes sense as it is essentially a souped up handheld. Though it's tough to ever count out Sony when it comes to home consoles.
I think it'll be something like PS5>Switch>>>>>>>>>>>>>>>XB4
But it'll likely be extremely close between the two Japanese companies, with Nintendo gobbling up most of Japan and a healthy amount of US/UK, while Sony will thrive more in the rest of Europe and have a close to even split with NS and XB in the US.
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