I think if you look historically, it is considered a failure at least imo if it continues at this slow pace in sales and doesn't pick up before the next generation.
When I look at the chart http://www.vgchartz.com/analysis/platform_totals/ I see a line between what is considered a 'failure' and the 'success' in consoles at least perceived by at least imo.
The line is between the SNES and N64 for me, where consoles including the SNES and above are considered at least moderate successes, while consoles below the N64 are considered at least moderate failures (outside of the just released Switch).







