So Nintendo might possibly sell 6M Switches at launch, right out of the gate.
In terms of revenue, that would be enough to eclipse the iPhone 6 launch from 2014:
https://www.apple.com/newsroom/2014/09/22First-Weekend-iPhone-Sales-Top-10-Million-Set-New-Record/
For the record, the iPhone 6's launch was international but not global. Some countries could only buy the device later in the year. Still, it would be a monumental occasion if a console manufacturer would launch a new console whose success is superior.
6M units at 400 USD a piece (factoring in the Japanese price) is equal to a 2.4 billion USD revenue.
GTA VI would need to sell 24M copies at 100 USD each to beat that start. That's looking increasingly unlikely.
Edit: yeah, 6M is not happening but what do you think about the actual tally at launch,
@Welfare ? Could it actually be higher than 3M?