This is how I see it.
Let's assume the final instal base before the 9th gen comes rolling around will be around 250m (similar as it is today; fewer casuals will buy consoles, but the gaming market has been growing steadily since 1985 and will continue to do so imo), and taking into account that XboxOne is $100 more expansive than PS4 and that PS3 has caught up to Xbox360 - even though launching one year later and costing more, I think it's safe to say that XboxOne will have a much slower adoption rate than PS4.
In the year 2020, if the casuals buy into the XboxOne multimedia thing:
PS4: 100m
Wii U: 50m
XboxOne: 80m
In the year 2020, if casuals DON'T buy into Xbox multimedia functions:
PS4: 110m
Wii U: 60m
Xbox: 60m
In the year 2020, if Sony comes to dominate:
PS4: 120m
Wii U: 40m
Xbox: 50m
In the year 2020, if Nintendo gets their shit together:
PS4: 100m
Wii U: 80m
Xbox: 60m
I'm on Twitter @DanneSandin!
Furthermore, I think VGChartz should add a "Like"-button.
