Skullwaker on 23 February 2015
I'm gonna guess by the end of the 9th gen. They'll continue remaking old games, which will sell, and next gen will probably have a few new entries. If we assume each of them sell 4 million, that would be 12m in new games and I think remakes + spinoffs could make up the remaining 6m. Of course, this also depends on how much their 9th gen system(s) sell.
Edit: And this is assuming Zelda U and MM3D sell 0 units, as I forgot to include them in my mathematics. So if we assume that between Zelda U and MM3D they sell a total of 8m lifetime (5m for Zelda U and 3m for MM3D, both safe predictions, imo) then they would only need to sell 10m units in the 9th gen, which is extremely doable.
