Zenmax have promised that TESO World would feel adventurous like in single player games. However, this will not be possible if they add world tiering, i.e. specific zones for specific level range. Getting to a higher level and going back to a low level zone would no longer make it feel like a "world of danger" or "world of mystery" (or "world of relevance" for that matter); rabid wolves and angry cave trolls would no longer be seen as dangerous monster, but instead low level mobs.

On a side note I'd like to add that if their monsters are to truly feel monstrous, they need to have their aggro range tremendously increased. Think of Skyrim or Oblivion and the times when you peeked out from behind a tree to see if that lion was still there and it spotted you from 100 m away and furiously ran towards you. Mobs simply can't wander around in their little sand-box areas and only attack you if you get really close. They need to behave like wild beasts, not just quest fuel that you grind through on your way to end game...

So how will leveling work without world Tiering? Well, there could be two or three tiers to separate starter zones from not-starter zones, but even if this could be avoided they could still implement a different leveling system. Let's do away with character levels and instead give them a certain cap in "perk" points (or skill point for that matter) that would be gained via reaching a certain threshold in experience. They have already mentioned such points and they could be used for whatever customization purposes they want, bottom line being that upon leveling up you don't gain a MASSIVE increase in stats, but just those few points and maybe a point in magicka/stamina/health (of your choice). This means your character is indeed getting stronger, but not that much stronger, and that you don't have to follow a certain path in your leveling process, but instead just go around and explore - much like is done in Skyrim - without the feeling that certain content is made obsolete after XX level.

And one last thing, they've mentioned that skills we put on our bars will level up progressively as long as we keep them and use them, but why not make it so completing a quest gives a certain XP bonus for the slotted skills? Also, there could be a cap of how many skills you can raise to max rank (or level if you will), so for example out of 50 (random numbers) available skills you can only max out 20 (with 8 being the maximum you can keep on your bar at any time) and in order to max others, you would have to "reset" some of the ones you have, slot the ones you want to level up and go do more quests. This would eliminate the part of the game where you say "Ok, I'm max level now, I'm DONE with the world! Where's the end game?!"

To sum it up, I believe these changes would make for a much more congruent world where you're not getting pigeon holed into one zone after another, but instead wandering at your own pace exploring the world and the areas you deem interesting instead of the ones your Pro XX Pro EXP Grinding Guide points you to.

And yes I know some people would just prefer to sit in one zone and never explore if they weren't forced to, but I say let them! A game should incentivize you, not force you, to see all of its content!

In one interview I remember Paul Sage saying that some areas and I think he was talking about instanced dungeons would require you to return to them later in your adventures and when you do the story of that dungeon continues and then you learn more about the whole thing....