Possibly, but it wouldn't be too far off now either. I suspect PS4 Pro sales are around 7-10M by now (around a third of the PS4 consoles in the US right now are Pros, for instance), so if the base consoles haven't passed the bar yet, they will do so very soon.
Yeah, I don't disagree at all that will happen. I was figuring around 10 million myself since Sony PR was stating 1 out of 5 PS4's sold have been the Pro model. And they were keen to point out that was during supply constraints indicating the Pro ratio might be even better with greater supply.
Anyway, my point was that it's odd for someone to say that if there was a release of a "Switch Pro", they wouldn't factor that model's sales into the lifetime sales of the Switch. That hasn't been the case for the PS4 Pro, the Xbox One X, the New Nintendo 3DS, or any other same gen hardware revisions of other gaming platforms.