My guess is that there will be 5-6 dungeons, and that sounds ideal to me. I think TWW had the perfect amount of dungeons, but OoT and TP had too many and MM had too few. What I would really like to see are a few dungeons that are very well thought out instead of 10-12 dungeons that are rushed just to add time to the game.
However, if they can pull off 8-9 dungeons that were still well done, I would gladly welcome that too. Given the amount of time that SS has been in development for, I think they could pull that off. Really, the amount of dungeons isn't a huge deal to me, but just as long as they are well-designed and creative, I'll be happy. Who knows, maybe we won't even see any dungeons at all. The development team said that they want to mix up the dungeon-field-dungeon method, so maybe that means that dungeons won't even exist. It's unlikely, but it's still possible.
However, I do NOT want to see a ton of well thought out dungeons but below-average sidequests. I don't want to see another TP, OoT or DS title, where the only sidequests are collectibles and trading quests. Those don't really add a lot of depth to the game and seem repetitive. I don't mind if they are included but SS also has to have many deep, and possibly emotional sidequests. If all of the development time was used for creating dungoens and a main story but no work has been done to add deep sidequests, I will be very disappointed.