Maybe for another game but not this one. It doesn't fit with their ideas or audience. The game is meant to be easy to access and allow you to do other things. Sure a zone like that would work for people that want it but there are many who don't want to invest full concentration while leveling. Etc.
timeless isle rares a good example -whilst anyone with raid gear can steamroll them fairly easily, someone in questing greens and blues fresh to the island can have significant problems and for blizz to try and program it so that rare mobs only hit geared players harder is not easily done.
i like the idea of level scaling overall though, but not forced i.e. the rift mentoring system, not the guild wars zone scaling. that way if you want to go and do loremaster but not faceroll your way through it, scale yourself down to the correct level, or even a few levels below (to allow for gear). it's been proven that the scaling tech is ingame through the instance bug reported on the forum (and front page a few days ago). so there's certainly potential.
more dynamic content - i.e. things that happen when you step on something, approach something, go through a doorway etc are always welcome in my opinion - like the falling wall thing, it's essentially like a rare mob frontal cone, but initiated by a structure instead.
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I think most of things I'm suggesting are things that people are already used to dealing with (don't stand in stuff!). It's the reason it's being added that's most important to me - It makes us pay attention, and it could possibly prepare some players for things they could expect in a raid or dungeon environment.
I agree that there should be more danger in the world really. I remember the days of Stitches in Duskwood, or Morladim, where you really have to watch out for them cause they could easily kill you.
Or that annoying patrol in Eastern Plaguelands. Nowadays you really have to try to get killed, at least in Vanilla zones.
I'd like to see more elites, or even a new type of elite that is a level higher, champion elite or something.
Well if you are wanting things to go this route then the one thing you forgot to add to the list is that once you die, you have to re roll a new character and start all over again from level 1..
It kinda sounds like you want the Timeless Isle.
I support these ideas. There definitely needs to be more danger in the world. My philosophy is that i'd like challenging content, but I don't want this challenging content to take up time that I do not have. So simple stuff like dynamic events added to the world would allow me to face some challenges in the open world, as I'm playing normally, without having to dedicate say a specific night to facing challenging content. I especially like the third idea - imagine packs of wolves that can track you down. You'd be able to hear them coming from their howls, and when they get very close passive mobs like deer might flee the area etc.
Then make the other ideas you have in the OP opt in as well so as to not force it on others who don't want the added danger.