Dont be a WoW clone. Most if not all games that have tried to clone wow have serious issues or fail outright. Devolpers do not understand that WoW's success doesnt lie in its game mechanics. It's success comes from a perfect storm. When it was released the cheap $300 emachines hit the market that could play WoW (albeit poorly). Also, at the same time, social sites like Facebook, Friendster, MySpace, etc (I call them the My Friend's Twit Face sites) came into their own and made spreading the word alot easier. Put those two things together and add the huge Warcraft fanbase and you got a perfect storm to have a hugely successful game.
I dare say if someone made a game, having basic game mechanics with the same perfect storm happening again, it would be hugely popular as well. WoW didnt really do anything new. They really did not make any big advancements in the MMO game mechanic. Had it been released a year prior or after this perfect storm, my opinion is, it wouldnt have been near as successful.
So please Zenimax or Bethesda do not try to copy WoW. Yes some game mechanics work. But outright cloning of the game, I feel will be a huge let down. The biggest complaint I have seen on forums for WoW clones is "I wanted something less like WoW". This includes the graphics. I think its been done to death. Alot of people are bored of them. Bright cartoony graphics are fine every few games but making every game since WoW this idealized look is old. Recent TES games have always been dark and shady. Make sure you keep that dark shady look.
Be ground breaking. You have the perfect mechanics for SPRPGs right now. Try to find ways to break them into the MMO world. The class system, xp system, etc are all different and a nice change from the current stagnant systems in MMOs.
Dont use commendations or make a gearcentric game. Yeah loot is fun. Loot is great to get. But making a game where gear is the only carrot is..... well..... boring! All you do is set up the game with X tier gear then over time you keep moving the carrot further out over and over. Nothing new. Nothing interesting. Just more grinding to get better gear so you can grind to get better gear so you can grind to get better gear. Its freaking BORING!!!
Add in secondary things that people can devote their time to in order to get loot. Things like dedicated crafters. Yes I said that. A class or classes devoted, not to the main story, but in making/crafting items. Add minigames like hunting and fishing. This is one biggie to me as my favorite thing in the TES or FO games is to go out hunting. Skyrim made this really amazing to me as I would spend hours a day just running around hunting deer. I know alot of others did so as well. Put in player housing. Yes I said that too. Too many MMOs now seem to brush off this part of an MMO as being unneeded. But its apart of the TES world. You always want to get a house. So make sure they are there. But it has to be very robust. Alot of detail. People will spend hours a day playing Barbie Dreamhouse. Instanced housing comes to mind here. Put them in the cities. Even put cabins in the woods people can purchase. If its instanced, many people can be clicking on the same door.
Try to get rid of the trinity. I dont know how. Just try. Too many games rely so heavily on the trinity. Maybe leveled instances (if you use instances) that would allow people to go in alone, with a friend, or 4. This way people dont have to sit and wait for hours on end for enough people to get on to get a group. Technology has advanced so much. I dont see it being any more or less difficult to make an algorithm that checks who is in your group and sets up the instance accordingly.
Speaking of groups versus solo. This is always a huge argument in MMOs. Dont fall into that trap. Both playstyles can work equally well together. Dont let it become the big win all be all of this game. Make content that levels accordingly (see above paragraph) and it becomes a non-argument. Just make sure the risk versus reward is working correctly. If the risk/reward is set up right people will still want to group. But wont feel "herded" into it.
PVP is the next thing. I like a good round of PVP as much as most. But PVP can make or break a game. The best thing I can think of here is dont segregate players onto PVP or PVE servers. Set up a system where players that want to PVP can do so on the same servers as the PVE players. Maybe a flag system that players, wanting to PVP, can turn on to PVP. This would allow PVE players the freedom to move around without harrassment. And the PVP players can gonk each other all they want. Honestly, IMO, PVP players that want to gonk PVE players are just griefers that want to hide behind a game mechanic. True PVP players want to fight other likeminded players for the challenge.
Anyway these are some of the things I hope TESO avoids or does. Again its only my opinion. So take it with a grain of salt.
Res