It's possible the teams that have already released games on Wii U are currently working on games for its successor to release in 2016-2017. Nintendo has recently stated they are working on a 3D Mario but didn't specify what platform, it could very well be for the next-gen device and be a holiday 2016 launch title. Outside of working on DLC, the Mario Kart team is probably already working on the next installment which could be a Spring 2017 title. We have seen a trend of Zelda remakes releasing every 2 years (OoT-2011, WW-2013, MM-2015) so its very probable Twilight Princess HD is being planned for summer/fall 2017. Retro studios said they got started on a new project when DKC released, they also release a game roughly every 3 years (Prime-2002, Prime 2-2004, Prime 3-2007, DKC:R-2010, DKC:TF-2014) so a new Donkey Kong or Metroid game by them is probably going to release late 2016 or in 2017.
Also I truly believe Nintendo is going to go the route where the next handheld and console share a library so this will also help with releasing games in a timely manner.
Yes, these are things (except the second paragraph) that I have taken into account and you may notice that all of your expected development times result in game releases in late 2016 or early 2017. So a launch before holidays 2016 isn't feasible.
As for the second paragraph, while I do think that quite a few games will indeed be available in more or less the same form on home console and handheld, I doubt that the entire first party lineup will be identical. Think of it in the Wii and DS manner where different control inputs made it impossible for some games to appear on both, even if both systems had been equally powerful.