I would say anything under 40mil. N64 and GC were considered flops and they both sold less that than. Also if the system is constantly missing sales productions then yeah. Also take into account prior gen.

It needs to account for a lot of market share. 21 million is a failure when your competition sold over 100mil. It would need to sell at least 50 million, since the market is large. 21 would only be good if the highest selling console is no more than 30-40 million. Selling only 21 million is not a profit if you shipped twice as many consoles.

A console that turns profit is no gigantic failure in my opinion. If you compare Wii U's numbers to the install base of Wii though, the console will certainly be considered a failure, even if it turns a slim profit.

8.5m. This number will increase when the Vita gets more sales.

It needs to sell atleast 30 million while profiting at the same time ...

20 million seems about right.

More than its dirrect competitor.

about 30M with profits.

It all depends? At what point is the console profitable? What did the previous console sell?

You can't define it by a certain number.

healty marketshare + big enough to profit

35-50m this gen. anything below is kind of "fail"