Unless they have a lot of surprise Wii U game announcements for 2016 other than Zelda I don't see how they can keep it going until 2017. It's not desirable but this really is a case where it looks like they may have little choice but to break the normally sacred 5 year minimum cycle.
Microsoft did the same thing and it really didn't hurt the 360.
It's actually not a *bad* holiday lineup (outside of Japan which is missing both Xenoblade and Wooly World since they have both already), it just lacks a marquee game. It'll be bad-ish for sales, but Wii U sales aren't a priority for Nintendo any more, and clearly haven't been since the push in 2013 failed to make much headway.
For existing, NA owners: Yoshi's Wooly World, Animal Crossing AF, Devil's Third, Fatal Frame V, Mario Tennis, and Xenoblade Chronicles X. Definitely a range from superior to bad games in there, but also a fairly diverse lineup. Just nothing that will light up the charts.