I'm mainly hoping to see the games that I was planning to buy from the VCs on Wii U and 3DS if this didn't happen. Some games on that service probably have a higher chance of appearing than most other games.
For regular Game Boy, three I was considering were Balloon Kid, Kid Icarus: Of Myth and Monsters, and Kirby's Pinball Land. I never did pull the trigger on them, since I've a feeling they'd be the sort of curiosity I'd enjoy playing once, and then that would be enough for me. These kinds of games are perfect for the NSO service.
For GBC, because Nintendo's able to get ahold of the Tetris licence again, I hope they don't stop at just the original. There was also a GBC version called Tetris DX and it included more extras than just color. I was also curious about Blaster Master Enemy Below. It looks similar to the NES game, but the level layouts appear to have some differences that could be neat to see.
I'm more interested in the GBA prospects. One game I really hope we see is Zelda Four Swords, since now it could be played online. I always thought this game looked pretty neat, but I never had the means to try out any version of it. Since they're getting Kirby Tilt ' Tumble to work, I'm hoping we'll also see WarioWare Twisted! and Yoshi Topsy-Turvy, those two games also look inventive. I've heard good things about the Sonic Advance games, since Sega's already involved in NSO with the Genesis offerings then hopefully they'll play nice and allow some GBA stuff as well. Drill Dozer looks like a fun puzzle game. I'm curious about the changes in the remake Kirby's Nightmare in Dream Land, as well as the more subtle ones in Super Mario Advance 2: Super Mario World.
There are probably some more I'd want if I gave it some thought besides what was on the previous VC.