To be fair, thinking it over, it's not like there's a TON of GB/C games left from Nintendo themselves worth putting on the 3DS, maybe save for some Pokemon games (did Pokemon Pinball ever get added?). Though SNES & maybe NES have a decent amount of games (mainly 3rd party) that could be added.
3rd party GB/GBC games I'd still like to see, even taking out obvious non-starters like mainline Pokémon, Dragon Quest or every licensed game ever:
Kirby: Tilt'n Tumble (Nintendo)
Pokémon Pinball (Nintendo)
Wave Race (Nintendo)
X (Nintendo)
Double Dragon II (Arc System Works)
Nintendo World Cup (Arc System Works)
Kwirk (Atlus)
Revelations: The Demon Slayer (Atlus)
Great Greed (Bandai Namco)
Mr. Driller (Bandai Namco)
Chikyū Kaihō Gun ZAS (D Wonderland)
Adventures of Lolo (HAL Labs)
Trax (HAL Labs)
Battle of Olympus (Imagineer)
Hammerin' Harry: Ghost Building Company (Irem)
R-Type DX (Irem)
Penguin Wars (Kadokawa Games)
Daikatana (Kemco)
Deja Vu I & II (Kemco)
Shadowgate Classic (Kemco)
Azure Dreams (Konami)
Bomberman GB (Konami)
Bomberman Quest (Konami)
Bonk's Adventure (Konami)
Bonk's Revenge (Konami)
Castlevania II: Belmont's Revenge (Konami)
Gradius: The Interstellar Assault (Konami)
Kid Dracula (Konami)
Metal Gear Solid (Konami)
Milon's Secret Castle (Konami)
Nemesis (Konami)
Operation C (Konami)
Parodius (Konami)
Pocket Bomberman (Konami)
Pop'n Twinbee (Konami)
Survival Kids (Konami)
Monster Rancher Explorer (Koei Tecmo)
Ninja Gaiden Shadow (Koei Tecmo)
Spanky's Quest (Natsume)
Penguin Land (Sega)
Rolan's Curse (Sega)
Rolan's Curse II (Sega)
Bubble Bobble Part 2 (Square Enix)
Classic Bubble Bobble (Square Enix)
Elevator Action EX (Square Enix)
Final Fantasy Adventure (Square Enix)
Final Fantasy Legend (Square Enix)
Final Fantasy Legend II (Square Enix)
Final Fantasy Legend III (Square Enix)
Magical Chase (Square Enix)
Sagaia (Square Enix)
Blaster Master Boy (Sunsoft)
Trip World (Sunsoft)
My NES and SNES list would make you weep.