Niek, I really like the idea of minidungeons!
We'd discussed a teleport item (an instrument) for a while back in the item development stage, but I guess it got completely lost! The method honestly doesn't matter, so Deku Nuts seem a great idea, since they fit with the theme. The only thing I'm wondering about is the limited number, how this will work. Are they just like any ammo-type item, where you find them in bushes or whatever and can only hold a certain amount? If so- then Gale Seeds from OOX would be a good way to look at this.
The only thing with this is that if we make them like gale seeds, then using them to escape dungeons could become a problem. I mean, the whole point of this utility is to allow a player to leave a dungeon at ANY point, to restock health/ammo, or if they get stuck, to get out. However, if the player needs to restock their deku seed ammo in order to get out of the dungeon, it seems backwards? Just something to consider- what does making them limited in number add to the game?
As for the beacon being mini-dungeons, I think this is genius! For one thing, in many Zelda games, mini-dungeons, though fun, just have rupees at the end and I'm always like - "more rupees? I already have a full walllet!" So having a legitimately useful reward for these mini-dungeons would be really exciting! The challenge with finding a new teleport spot is cool too, I was always really excited in twilight princess when those monster dudes showed up because it meant I could teleport here soon.
The only thing to note here is that we have to make sure that these mini-dungeons are marked clearly enough that they aren't too hard to find. Teleport spots need to be kinda by the main path to be useful, so this should make them easy enough to find. What if we graphically mark these mini dungeons? Like, the entrance is always an arch with a certain symbol, like the shiekah eye, in the keystone.