My guesstimation is 18 to 20 million. I doubt it will beat Gold/Silver since as others have mentioned, there's a new Pokemon game every year and also because at present, it doesn't look ambitious in it's scope.

Since Let's Go already hit 10 million, I would say it's safe to assume Sword/Shield will nearly double that amount but maybe the nostalgia value is far more stronger for Let's Go?

First place, the other Pokemon games are not impressive. This one will easily sell 100 billion units.

It definitely has a chance to beat G/S. Can't say for sure as yet though, there's not enough info and it's too far away to have properly had people board its hype train. ATM I think it'll do around 20m, but if it looks good as more info comes out, it could go 25-30m maybe even more.

Between Diamond/Pearl and Gold/Silver.

Unlike Pokemon games of yesteryears, they just don't get time to breathe. Nintendo games are known for awesome sexy legs too. Seems counter-productive.

Switch is another beast though. 15 million is the floor. I'm estimating 19 million.

I picked 4th because there is no way that you can be 3th, 2th, or even 1th in anything.

To be serious, though, I think that the legs of the game will also be cut off by having a straight-up improved version come in just a year after launch, though I hope that spot will be taken by a D/P remake instead.

VGC has Sun/Moon at 15.17m and Ultra Sun/Moon at 7.15.  That total is 22.32m.  To me that is the ceiling for Sword/Shield.  I think it will do close to that but not more.  That actually puts it just below Gold/Silver, but above all of the other games (except the original).

If you count USM you should count crystal as well for Gold/Silver

But I agree that USM has cut the legs of S/M way too much as it released too ealy, S/M would have done around 18-19 millions witout it.

You may be right, but it wouldn't change my result.  I still think Sword/Shield will sell less than Gold/Silver.  I'm mostly trying to determine a ceiling in case there isn't a third game or equivalent to Sword/Shield.  X/Y didn't have anything like that.

Very difficult to guess. Could go any way. Still, I think if it was a bit more ambitious, it would be easier. For now I'd say it'll end up above XY, at say 17m.