A second trilogy is very likely. I really doubt the whole trilogy will make it to the Switch though.
Basically it will probably be like this....
Metroid Prime 4 - Summer 2019
Metroid Prime 5 - Holiday 2021
Metroid Prime 6 (not on the Switch) - Holiday 2024
So a very similar release pattern to the original trilogy.
Lifetime Sales Predictions
Switch: 156 million (was 73, then 96, then 113 million, then 125 million, then 144 million, then 151 million)
PS5: 115 million (was 105 million) Xbox Series S/X: 48 million (was 60 million, then 67 million, then 57 million)
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima