I think it's better to dedicate a thread were people think that the psvita is doomed instead of 1000 topic about this subject people can make the reasons of psp is doomed and all psvita doom articles.
PS4 - over 100 millions let's say 120m
Xbox One - 70m
Wii U - 25m
Vita - 15m if it will not get Final Fantasy Kingdoms Heart and Monster Hunter 20m otherwise
3DS - 80m