I reckon at least 9, I think they want this to be a definitive Zelda, so therefore it can't have fewer dungeons than OOT or TP

They should make the dungeons randomly generated then they could have as many dungeons as they want and it would be different every time you enter, making them literally countless different dungeouns. That would be so awesome

That would be interesting, but pretty hard to pull off in a 3D environment. I suppose it all also depends on whether the game is going to be truly open world(no loading screens minus the intial start up) or a mix of a giant sand box with a bunch of holes, so to speak.

Actually the definition would be "instance separated from the world map, though accessible by it" or something like that.

Your definition of a zelda dungeon also lacks a mid boss =p

depends on the concept of dungeon.
some of them will be on open world, you use the sailclock and drop on a piece of land that is also a "dungeon".
closed dungeon, i guess, 6.

I've only ever played (and beat) Wind Waker HD so I'm in no way a Zelda pro

I'd say 8 dungeons shall be a good amount. Hopefully, they put in a ton of side things as well.

Ocarina of Time has 12:
1. Inside Great Deku Tree
2. Dodongo's Cavern
3. Inside Jabu Jabu's Belly
4. Forest Temple
5. Fire Temple
6. Ice Cavern
7. Water Temple
8. Bottom of the Well
9. Shadow Temple
10. Spirit Temple
11. Gerudo Training's Ground (optional)
12. Ganon's Castle

Your definition makes every house and shop sound like a dungeon =P

His definition would eliminate entire Zelda games, including the original, due to no boss keys. Also compasses aren't in all games as sometimes the map just tells you everything you need to know. I think some games don't even have you collect the map. Link Between Worlds didn't even have the new item in the traditional sense. Some games have little in the way of puzzles beyond pushing one block, lighting torches with no trick to lighting them, or killing all the enemies, and that's not really having puzzles at all. Really none of his criteria are universal to all games, they're all broken at times. Zelda II breaks all of those conventions at once.

I'd say it's a separate instance of game space in which Link traverses enclosed areas (rooms) with various game mechanics driving progress through the rooms, including enemies and built in mechanisms (e.g. pushed switch, lit torch), ending in a boss fight. Non-separate or non-enclosed would make it like Skyward Sword's overworld. Lacking enemies or the other dungeon traversal mechanisms, or lacking a boss, would just be a huge disappointment for a main dungeon. Mini dungeons need not have a boss or even enemies but wouldn't be recognizable as dungeons without the other criteria, and would still need an end goal to replace the boss and define the end of the dungeon.

Probably millions.

it's a big game.