The 3DS/DS NEVER sold this bad.
And that means nothing. When the DS was selling terrible in 2005, people thought the system was doomed because the GBA never sold numbers that low. Then when the PSP came out and was actually outselling the DS by a large margin each month, people took it as a sign Nintendo had finally lost it's handheld market and that their audience was going to move on to the PSP. Despite the fact the DS big games hadn't been released yet and the PSP was aiming at a different demographic then Nintendo handhelds, people still declared the system was finished.
And yet when the games where finally released for the DS at the end of 2005, sales increased by a lot. Of course, even then the sales didn't truly lite on fire and become the monster it would be until the DS Lite and New Super Mario Bros were released in Summer 2006.
So it doesn't matter if the Wii U sales are lower then any previous Nintendo system right now because the system has no current major titles and is too expensive. Once the games come out this Fall, and the price is hopefully cut the sales will finally increase. I don't know why this is so hard for some of you to understand? Now if the Wii U is still selling this bad next year then yes, the system will be fucked because it means Nintendo's big titles had no effect. But right now, it's way too early to say the system is doomed when several of their biggest franchises have yet to be released and were huge hits on their previous console and currently huge on the 3DS as well.