By the time it's finished, Switch will more than double Xbox One's lifetime sales I reckon.

oh yeah for sure. Xbox One will probably limp across 50 million in 2021 and never reach 51 million. Unless something catastrophic happens to Switch it should still have life left in it when it passes 100 million.

It should be around 2.5-2.6x, as the xbox one is unlikely to even reach 50m.

Yeah I expect it might hit 49 million next year, though only getting to 48 million is certainly possible, maybe even likely. I'd guess it will sell a million systems after 2021 by people who finally decide to pick it up on the cheap. So 49 or 50 million lifetime is most likely. and 48-49 million by end of next year.

At this point, I'm still thinking at least triple.

That would require something unprecedented.

Last year into early this year, I used to think Xbox One would finish at around 55 million, now I'm not even sure it'll make 50 million.

It would require something unprecedented.  Nintendo would have to do something exceptional like unify home and handheld platforms onto one system. 

Dude, you're talking about somewhere within the 140-150 million range. 

The Switch is doing amazing, but let's not get carried away here.

Well, I made this thread about 2 years ago and I still stand by it.
http://gamrconnect.vgchartz.com/thread.php?id=234359&page=1

I still think all of the handheld market plus most of the home market will buy a Switch.  I definitely don't think this year is the peak year, not by a longshot. 

One thing I will say though, people have this image of the PS2 being unbeatable.  Historically speaking, some home system becomes "the best selling yet" about half of the generations.  Half the time the record gets broken and half the time it doesn't.  I think this time around Switch is going to break the record.  This sort of thing happens a lot more than people think.