If nothing else, we can safely expect a Mario Odyssey blowout, Mario + Rabbids Kingdom Battle, more Splatoon 2, and a final push for ARMS. Fire Emblem Warriors and Xenoblade Chronicles 2 are also extremely likely, having been repeatedly confirmed for 2017 (be that the calendar year or fiscal year).
As a "worst case" scenario, that's not shabby at all.
But there's also plenty of smoke to suggest probable appearaces by Smash Bros, Pokémon Stars, Pikmin, the Virtual Console, GCN games, perhaps Mother 3... Also, the timing is right for Retro Studios and Animal Crossing.
Certainly there are more "safe bets" to speculate about this year than the last couple E3s, between the leaks and rumors and perfect storm of first-party development cycles.