Of all my complains about the cross realm zones, that are not technical of course, my biggest one is that it is a lazy solution to a much bigger problem that blizzard created for themselves.
The main intent that they say the cross realm zone is for is to make the world seem a little more alive while leveling. Lets forget for a moment that it creates all types of problems elsewhere like people trying to do the achievement yesterday with people from five or more different realms all on mammoths standing on the NPC while flagged for PvP on a PvE realm looking to grief people that just want to get an achievement and have some fun. This alone is reason enough to say the CRZ idea sucks, but that is really just a side effect to what they are, or say they are, trying to do. Bring life back to the leveling areas.
Well, the solution is actually a lot simpler than wasting man hours developing a cross realm system. Slow down leveling. The reason the lower levels do not see anyone while leveling any more is because people level way to quickly. That means they speed through leveling and usually have all the max level characters they would want. So that means they reroll less often than they did before, which means less people out there leveling. Adding to that super fast leveling is the dungeon finder where you can level from 15-85 without ever leaving a city if you were so inclined to do so.
That is a self made problem. They made leveling so fast it is blink and you miss it. They allow low level dungeon finders to level people without leaving their home city. They created this problem and now they are using a lazy solution to attempt to fix the error they made.
The world is empty because that is what they designed it to be, empty. They made it so people will not be out there. If they wanted to fill the questing zones they could do that if they put a little more effort into it instead of taking the easy way out and condensing everyone onto the same server.
Slow down leveling to the point where it would take considerable time again. The areas would be full of people if people weren't speeding through them. It works on many levels too. Not just the speed of leveling through a zone but if you wanted to reroll it slows down the reroll process. So instead of you leveling 5 new classes in one month, it would take a year or so to level them all, thus making the world look fuller from your participation alone for one year instead of one month. That is part one of a better solution.
Part two would be, give people a reason to get out in the world again. There are many ways to make low level zones something everyone would want to visit but instead of building a new design to professions, which would require more materials from all over the world at all levels, they went the easy route of cross realm. Instead of adding more world events that would make people get out, think the rifts in rift and their rewards regardless of level so all would want to do it, they went the easy route with cross realm. Instead of adding achievements in those zones for achievement hunters, even if they were as simple as fish 1000 fish in X zone, they went the easy route of cross realm. There are hundreds of ideas that would get people out in the world if they just took the effort to add them, but they went the easy route with cross realm as a fix all for everything.
Another part is the random dungeon finder. Lower the experience so low that it would not even be worth doing it unless you have a quest there. While dungeon leveling is considerably slower than leveling it is not so much so that it turns people off from doing it. As long as many of the players think of it as a viable leveling option, even if they are wrong, they will not go out in the world if they feel they can level efficiently while standing in their home city.
I can see why they do not lower the dungeon experience and make the leveling take a lot longer, they fear backlash from the players. The reason for this cross realm zone is to cover up for the fact the world is dead in part to them losing players left and right. So they do not want to take the chance of scaring more off.
The fact they are missing is a fair deal of players that left the game probably left because of the speed of leveling. When they reached end game at the beginning of cataclysm and it was too hard for them, they went to level an alt and they were maxed on that too fast and were in the same position they were before. End game with nothing they could do. Slow or fast, they would lose people, but at least slow leveling would make the world look more alive and keep people playing longer.
Even if it is the fear of scaring more people away that does not change the fact that cross realm zones are a lazy solution to making the world look full again while leveling. The real solution would be to make the world full again while leveling by adding content, making people spend more time in that content, and making it worthwhile to be in those areas.
If they really wanted to make the world look full again they would slow down the leveling experience a fair deal, create a lot more content that is worth doing in those areas, and give people a reason to be there instead of staying in a city. But instead of creating quality content to get us out in the world they decided to use the cross realm zones to try and make it look like more people were out in the world, and it still doesn't. If you have leveled a new character recently you will know that for the most part the world is still completely empty most of the time. Starting zones are the only things that seem more alive.
So the world does not really seem more alive because of the cross realm zone except for those moments like yesterday at pirates day when 5 servers worth of people all decided to grief people just trying to have fun during a holiday event by being on top of the NPC with their mammoths while flagged for PvP.
This is proof that not only is the cross realm zone a lazy solution but it is also the wrong solution.
In the end, if blizzard really wants to make the leveling world look full they should have created content to make the players want to get out in the world and not tried to cover it up with a lazy solution.