I think Nintendo is in the best position here since they've just released a new console and so far the mass majority of the games they've announced for it all release before the end of 2017.
I expect details on upcoming games they've already announced such as Xenoblade Chronicles 2, Super Mario Odyssey, Fire Emblem Warriors, Fire Emblem 2018 and Splatoon 2.
For games they've yet to announce releasing before 2017 ends, I predict a third Sun and Moon game for the Switch, Super Mario RPG X Rabbids, Mario Maker for Switch, Super Smash Brothers for Switch and the announcement of the virtual console with games ranging from the NES to GameCube (or maybe even Wii).
Now for games releasing 2018 and beyond. If I know Nintendo, it's that they love to announce games which are releasing way later on (even if it's just a non title final) examples being, Zelda Breath of the Wild, Tokyo Mirage Sessions ♯FE, Starfox Zero, and recently "Fire Emblem Switch". Here Nintendo is very unpredictable, they could announce some of the most random things you never even thought and may blow your mind. My guess on something which is likely is Animal Crossing, Something Mario related, a HD remake/premaster of one their previous games.
Third party wise I expect Nintendo's e3 2017 to have the best third party offerings they've ever had (even if it doesn't say much). I expect details on Shin Megami Tensei 5, Dragon Quest XI, Sonic Forces, Skyrim, and other details and mentions of games we know are coming. As for completely new announcements third party wise, I don't have much of a clue but are possibilities could be Switch Monster Hunter title, Rocket League, Beyond Good and Evil 2, Overwatch? Bayonetta 3? Dark Souls Trilogy? Mostly at least details on one title from the 3rd party Switch developers list which have yet to say what they are bringing.
I'm not exactly sure what Nintendo's E3 show will be like this year, but one thing I do know is that it has the potential to be Nintendo's biggest and greatest one yet!