I found out about this a few days ago. To be honest I felt skeptical about it. On one hand I was happy to see another Zelda game out, yet on the other hand I questioned about it looking more like an enhanced remake than an actual sequel. However, last night after realizing that Eiji Anouma was behind the project too, I remembered a Skyward Sword related article that hinted about a possible Link to the Past 3D remake. I put the pieces together and came to the conclusion that it is a sequel cleverly disguised as an enhanced remake of the original game, which is a unique twist.
I doubt that Ganon and/or Agahnim will be the main antgonist(s) considering how they were both killed previously, but anything can happen. Still, I doubt Nintendo would do a rehash of the same story. They always go with the "same characters, difrerent settings" approach and direct sequels do appear once in a blue moon.
Ocarina of Time->Majora's Mask
Oracle of Ages->Oracle of Seaons (or vice-versa)->Link's Awakening
Wind Waker->Phantom Hourglass->Spirit Tracks.
Also on a curious note, the "Decline of Hyrule" timeline on the Hyrule Historia Timeline actually has the most sequels out of the 3 branched timeline stories with 6 games total (now 7 Counting the ALttP sequel).
Sorry if I'm nerding out about this. I just found it interesting to share.
Overall I'm mainly interested in the story this time around. We'll just have to wait and see what else will happen.