I have to be honest, 500k for Switch this month doesn't looks as crazy as i thought before... i still think 400-450k is more realistic, but Nintendo is on fire right now.
That said, i believe that for November/December Nintendo may have better sales than 1 million per month... maybe 1.2 million per month? (About XB1 2014 holidays level)
That would be pretty insane, expecially since right now, Switch is having a way better year overall.