I don't believe next xbox is 2019. Holiday 2020 maybe. If halo infinite and gears 5 come out on xbox one first i believe they will be screwed next gen. They need to come out all guns blazing. Like never before or else they'll pale in comparison to their rivals. Halo infinite and gears 5 might be cross gen though.
I expect Halo Infinite and Forza 8 to be launch titles for the next xbox. Possibly crossgen. Holiday 2020. Gears 5 on Xbox One won't screw them.
Predictions (Made July 2019)
LTD: PS4 - 130m, Switch - 110m, XBO - 52m 2019 : PS4 - 15m, Switch - 18.8m, XBO - 4.8m 2020: Switch - 22m (Peak Year)