Looking only at 1st and 2nd party output over the last few years, I think you can form a few solid predictions of what to expect at Nintendo's E3 2017:
The Expected-
- We'll obviously get a deeper dive into Super Mario Odyssey and Xenoblade 2 and get a clearer idea of whether the latter will actually be releasing in 2017. If it is, I'd expect a December release.
- I think we'll also get a good look at Splatoon 2's story mode.
- We'll also likely get details on Zelda's Summer DLC.
- Kirby's holiday action title for 3DS will probably be revealed as well.
The Much Rumored -
- Of these two rumored titles, the Smash Bros port and Pokemon Stars, I think we'll get at least one for release in the late fall period. The Pokemon games are usually revealed 6 to 10 months before release, and typically not at E3, so if the Stars rumor is true, it will be interesting to see how it is revealed. If the Smash Bros port is revealed, and it has any new characters, I feel one is very likely to be an Inkling. Also, if Splatoon 2 is going to be releasing along side the online service app, I could possibly see a Smash Bros port launching when the online service becomes paid in the fall.
Animal Crossing Possibilities -
- Looking at EPD Group 2, the team that covers the Splatoon and Animal Crossing franchises, they have not released a mainline Animal Crossing title since 2012 (2013 in the US). It did receive a fairly large update in 2016, but it was free, and large parts of it were outsourced to other development teams. I wonder whether development for a new Animal Crossing had begun on the Wii U and was pushed to the side to wait for new hardware to come along. Meanwhile Happy Home designer was made as a stopgap title for the 3DS in 2015. The Animal Crossing Plaza on the Wii U was kind of a weird thing that didn't amount to much.
On top of this, the Animal Crossing mobile title reveal may have been delayed to tie it with the reveal of a new main version for the Switch. It's possible that the two titles may connect in some way. If Animal Crossing for Switch is revealed at E3, I'd expect it to be a Spring-Summer 2018 title. The main sticking point is how big EPD Group 2 is, and how much of the team they have working on Splatoon 2 and its future DLC.
Likely Reveals -
- There are two EPD teams which will very likely have at least one title to show off at E3, EPD Group 4 and Group 7.
- EPD Group 4 is in charge of the Pikmin and 2D Mario titles. Their last releases were Super Mario Maker in Fall 2015, and Pikmin 3 in Summer 2013. Pikmin 4 has been mentioned by Miyamoto several times, but with conflicting information - how the title is almost completed, but at the same time, how it has also fallen down the list of priorities. Seeing as it's likely this team will have at least one title ready in 2018, a reveal of either the Pikmin game, or perhaps a new 2D mario, will likely be shown at E3.
-EPD Group 7's last projects were Miitomo in 2016, which was co-developed, and the last Rhythm Heaven in 2015. I'd expect a new title to be shown at E3, whether a sequel to a well known franchise ( WarioWare would fit well on the Switch), or a brand new IP. Though I'm not sure how involved this team is in all the Miitomo updates.
The Greatest Mystery-
Finally, it would appear that Retro Studios should be ready to reveal something. I don't know what it could be. There were rumors that it was a new IP, but I guess we'll find out eventually. The main interesting piece of information about Retro Studios is that it took four years between their major releases of Donkey Kong Country Returns in 2010, and Donkey Kong Country Tropical Freeze in 2014, yet they also assisted on Mario Kart 7 and the 3DS port of DKC Returns during that time. To my knowledge, they have not done any assist work since the release of Tropical Freeze, and have devoted all their resources to their next title, or possibly, titles. We also know they love barbecue.