There are two ways to potentially improve on the World of Warcraft.
One is to make WoW a far more dynamic place, instead of the static world it currently is. But apparently Blizzard stated that will never happen because they want someone just starting the game now to experience the "same game" as someone who began playing a year ago. But that's jut a copout, rebutted by keeping "classic" servers, while adding new, dynamic servers. I think the zones known as "contested zones" on PvP servers could become a little more contested, and it would make the game a lot more interesting to people who enjoy the PvP style of play.
I'd love to see the Horde or Alliance be able to sack a town belonging to the opposing faction. Currently a few high level, Epic-clad players will storm an outlying town populated mostly by lowbies, slaughter the guards, then pwn the living hell out of any lowbies who foolishly fight back. This persists until enough high level players on the opposing team fly in and do some pwning of their own. Slaughtering lowbies is fun to some people, but they don't enjoy a dose of their own medicine. So when a real challenge shows up most people hearth back home.
But what if a large Guild descended upon a town, such as Darkshire or the Crossroads, pwnd the NPC Guards, planted a Flag in the middle of town, then defeated any resistance, including high level opponents. Then pwnd the NPC Guards again when they respawned, then soundly defeated a lvl 70 NPC Boss and several escorts when they turned up, all while fighting off opposing players. What you'd have is a situation not unlike a skirmish for a Tower or Keep in the Alterac Valley Battleground, only taking place in the World of Warcraft itself. And after sacking the town and defeating all comers, and holding the territory for a period of time, such as 30 minutes, the victorious players have a choice. They can keep the town, in which case it becomes a town under their faction's rule and the former owners now have to gather an army of their own to take it back; or the invaders can sack the town, getting some gold and maybe a few rare treasures, but their faction will not gain control of the town. In fact choosing to Sack the town will spawn an army of Elite Soldiers in the nearby capital City, wand unless the invading force is very large in number and very well coordinated, this army of Elite Soldiers will retake the town and destroy the invaders, driving them out of the town and making it a somewhat safe place once again. But with this being the World of Warcraft there is no place that's ever 100% safe.
But what if the invaders take the town? What about any quests you had from the townsfolk there? What if you'd set your hearthstone in that town? Simple, your hearthstone will be reset to the nearest capital city's Inn. And you can still complete the quests, but the townsfolk will have also taken refuge in that capital city, so you can find them there to turn the quest in. And if you're lvl 60 or higher, these displaced townsfolk will have new quests, asking you to talk to the city's leader, King, etc, about retaking their town. When you talk to the local leader you can get a Raid quest to help retake the town. The reward being some XP, gold, and an increase in Rep, and perhaps a Royal Tabard, ring, or necklace to show you are a loyal & willing soldier.
So, one way to improve upon WoW would be to allow PvP conflicts on a large, world-changing scale.
The other way? Borrow from Blizzard's own Diablo II. Go Hardcore. True Hardcore. Your toon dies, and that's it. You want to play again? Reroll.
Ok, considering there are classes with spells that allow them to resurrect other players, you don't suffer Permadeath if you can get a player to Rez you in-game before a certain time limit (like 30 mins or so). So there'd be no staying online for hours, waiting for someone to Rez you. 30 minutes pass by and that's it. You're dead for good. Reroll.
Imagine how white knuckle a Raid would be with everyone knowing that if they Wipe, almost the entire Guild will have to reroll and start back at level 1. Now while death would be permanent, you could essentially start the same toon over at level 1, sans all skills, items, & gold of course. This way you'd retain your toon's name, Guild Membership and Friend list, and more importantly perhaps, your Ignore List ;) but everything else would be reset. It would be a complete new start. I know what you're thinking. Have a Bank Alt, right? Send all your Gold, mats, spare items, anything not soulbound to your toon goes to the Bank Alt before you go adventuring. Good thinking. That way if you do die, your Bank Alt can finance you to help rebuild your toon. So the only real penalties for death would be reversion to level 1, and loss of any Uber Items associated with and being carried by that particular incarnation.
The one bug in this ointment would be the griefers. They'd be the players that get a kick out of ruining other players' days. Like the high level fellow that Ambushed me while I was crossing the bridge into Lakeshire and pretty much one-shot killed me. Yep, there really are folks out there who get a kick out of thinking they've ruined your day. In that situation I was more surprised than pissed off. Here I am, crossing the bridge into town. La la-la la-la. What the fuck??? I'm dead??? How the hell did that happen???
Check the Combat Log and...Stabby's Ambush Crits you for 1,427. You die. Well, duh! I almost died three times over from that hit!
Swim down the river, Rez under the bridge and trot into town, reminding myself that I am playing on a PvP server, so I've pretty much agreed to be one-shotted by sneaky Rogues like Stabby.
So that would be one problem with a Permadeath Hardcore Server. Fellows like Stabby hiding out in an area frequented by lowbie Toons knowing that everyone he kills has to start all over if they can't get a Rez within 30 minutes. And chances are Stabby is going to whack the guy attempting the Rez as well.
You could always play on a Hardcore PvE server, where you're not as prone to being Ambushed by Stabby & Co., but even on a PvE server it's very easy to die if you're not being careful. Hell, I died the other day and it was practically an involuntary suicide. I'd dropped off the Scryer Elevator in Shattrath, a survivable drop if you're at full health, but I wasn't at full health. I still survived but was left with barely 100 hit points. Running into the center of Shattrath I took the portal to Stormwind, which takes you to the top floor of the Mage Tower. Running out the door I did what I normally do when I exit the SW Mage Tower; I ignored the spiral staircase and took the fast way down. Normally when I drop off the Mage Tower I have a lot more hit points, so normally I'll hit the ground and keep on running. This time when I hit the ground I didn't get back up. Oops. That would be an embarassing Permadeath.
"Rerolling, huh. How'd you die?"
"Splatted off the Mage Tower in SW. All the Rezzers just laughed at me :("
"LOL! You noob!"
So we have two ways to potentially improve upon WoW. And Blizzard wouldn't need to change the entire game. Keep the current servers exactly the way they are and set up brand new servers (so everyone starts at level 1) with dynamic zones, where towns can be sacked & pillaged, or even captured. And set up brand new Hardcore Permadeath Servers where dying means a lot more than just a corpse run back from the local Grave Yard.