I'm not (really) hating on the N64 library here, but what would even be on this?
Mario 64
Both Zeldas
DK64
Wave Race 64
Smash Bros
Mario Kart 64
Star Fox 64
Up to 3 Mario Party games
Kirby 64
Yoshi
Pokémon (either Snap, or Stadium 2 if you could connect it to the 3DS VC)
F-Zero X
What good 3rd party stuff would they be able to get? The Rare games would be out of reach, right?
This is the list of the N64 games available on Virtual Console:
1080° Snowboarding,
Cruis'n USA,
F-Zero X,
Kirby 64: The Crystal Shards,
Mario Golf ,
Mario Kart 64,
Mario Party 2,
Mario Tennis,
Paper Mario,
Pokémon Puzzle League,
Pokémon Snap,
Sin & Punishment,
Star Fox 64,
Super Mario 64,
Super Smash Bros.,
The Legend of Zelda: Majora's Mask,
The Legend of Zelda: Ocarina of Time,
Wave Race 64,
Yoshi's Story,
Excitebike 64,
Donkey Kong 64,
Harvest Moon 64,
Bomberman 64,
Bomberman Hero,
Ogre Battle 64: Person of Lordly Caliber
* In italics the third-party games.
If Nintendo wants (so to not pay any license) they could easily hit 15-20 just with first-party games and maybe add a little bonus like OoT Master Quest.
Some third-party games would be nice though:
Resident Evil 2 (Capcom), Megaman 64 (Capcom), Castlevania Legacy of Darkness (Konami), Mystical Ninja Starring Goemon (Konami), Bomberman 64 (Konami through Hudson acquisition), Ridge Racer 64 (Namco for the series rights, game code is owned by Nintendo), Ogre Battle 64 (SquareEnix through Quest acquistion), Harvest Moon 64 (Natsume), Rayman 2 (Ubisoft) and of course some Rare stuff (Microsoft).