- the generation time for wii U will be lower than the generation time for ps4/xbo. i would say 5 year for wiiU.
- Some think that market will shrink. Without wii casuals, the market will be surelly lower than 7th. I would bet in something between 6th and 7th gen market size.
So, your min wii U prediction could be You min wii U prediction times 5/7.
And you could calculate again the minimum with a lower estimated market size.