It will still be Sony and Nintendo's market for the next year at least. Switch sales won't significantly drop until 2022 or 2023. PS5 will surely start stronger out of the gate than the Xbox Series X.
Lifetime Sales Predictions
PS4: 130 mil (was 100 million) Xbox One: 55 mil (was 50 mil) Switch: 110 million (was 73, then 96 million)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima