That 20m is shipped, so sell through need only be around 18-19 million. So far the Switch has sold 1.4m this fiscal year according to VGC, and it sold 170k on the latest update. If we assume it sells that much every week from June until November, that would be 3.7 million, for 5.1m total. This means Pokemon and Smash would have to push 13-14m systems in 5 months. I'm quite skeptical it'll happen, but we'll see!
EDIT: 3DS with the wombo combo of huge price cut, value saving bundle, SM3DL and MK7 still "only" managed 10m in the same 5 month period. Really don't think it's gonna happen unless Mario Tennis Aces/Octopath/Mario Party/etc. prove to be substantial enough that Switch reaches higher than 5m before November.