1. Zelda Collections
A collection including Ocarina of Time (3DS version), Majora's Mask (same), Wind Waker, Twilight Princess and Skyward Sword. All in HD and portable. And a 2D collection including the first Zelda, A Link to the Past, Links Awakening, Minish Cap and the Oracle games. All remade in a more modern style (like Ocarina on the 3DS).
2. Switch Sports
I loved Wii Sports to bits and so did my friends. A Switch Sports with better motion controls, online play and a big number of games would be amazing. Maybe some RPG elements (think Mario Golf on the Gameboy).
3. GTA V
I played GTA V on the PS3 but portability would be huge for this game. Having this on the Switch would be amazing!
4. 2D Mario
In my opinion 2D > 3D Mario. The games also sell better. Super Mario Bros. just needs a proper next entry: high production values, good graphics and especially better world-building than the New Super Mario Bros. series.
5. Zelda: Breath of the Wild 2
Doesn't really have to be a direct sequel, just a game that builds upon the great foundation of BotW. I'm sure the Switch could produce an even bigger and more beautiful game!
6. A proper Resident Evil game
I played Resident Evil 4 and 5 so many times but I haven't touched 7 yet. Having those games or a new Resident Evil on the Switch would be great.
7. Super Mario Maker 2
The first game was great and the only reason I'm not playing it anymore is because it's on the Wii U.
8. Advance Wars with local and online multiplayer
There are many more I could think of but that's all for now!