10 million lead over 3DS, awesome.
By this point 3DS had sold more than half its lifetime sales too, while Switch should be less frontloaded as it's only had one revision so far and the standard model is still $300.
In 2014 the 3DS sold 9.74m, so in 2020 Switch can tack on another 10m units to its cumulative lead.
In 2015 the 3DS sold 7.33m, so in 2021 Switch can tack on another 10m units to its cumulative lead because, like you said, Switch still has plenty of price cut and revision options left in order to stabilize its sales in the future. Selling 18m units in 2021 isn't really that much of a challenge.
In 2016 the 3DS sold 7.59m. Switch enters 2022 with a cumulative lead of 30m which is what curl-6 predicts to be the lead in lifetime sales in the end. So for 2022 Switch sales, curl-6 is predicting that Switch will fall off a cliff and then proceed to sell like the 3DS did late in its life. Note that curl-6 doesn't think that that qualifies as having a pessimistic outlook.
3DS in 2017: 6.63m.
3DS in 2018: 3.50m.