Not sure if this question has actually been asked before in this way. What do you want from D&DN in a broad sense and how would you do it? My big ones.
1. Easy to DM. Look at pre 3rd ed D&D for this and 4th ed as well.
2. Better class balance than 3.5. Doen't have to be perfect but it has to be better than 3rd ed.
3. Has to resemble pre 4th ed D&D at least on the surface. Alot more liberal on the mechanics.
4. Has to incorporate some of the positive changes 4th ed had.
Those are the big goal posts for me at least. How would I do it? I wold probably look at creating a fusion of 2nd ed and 3rd ed. Feats, skills, etc would be retained along with the pre 4th ed class structure which the current playtest rules indicates to be the case anyway.
Around about now I am probably going to bget my head bitten off for not appealing to 4th ed players needs. 4th ed is very different from BECM-3.5 but I think one can at least get some of the design goals from 4th ed regarding things like class balance encounters design and things like the recharge mechanic. Elements of 4th ed can be seen in the playtest packets beastiary and the current verison of the fighter class even though it doesn't have powers as such.
The classes and races would also be more inclusive. Some of the 4th ed posters here have indicated that on release 4th ed made a mistake in not having all of the 3.5 races and classes in the core book. 3.0 had al of the 2nd ed classes available day 1 for example. This means that the core book should have 14 classes (11 3.5 ones, Warlord, Warlock and Assassin) which the developers have already indcated is the case. That also means the Dragonborn will be a core race and if I were the developers I would add the Dragonborn to a future playtest packet sooner rather than later. At least get the 4th ed players interested and do it soon even f the Dragonborn is only based on the 4th ed one. When editons change personally I do not expect a 3.0 elf to be the same as a 2nd ed elf bt I do expect it to resemble one.
The current play test rules also indicate that vancian casting is coming back which is good for me but I understand other gamers do not like vancian. I do not no if they will have a non vancian wizard option in the PHB but 4th ed classes such as the Warlord and Warlock would be prime candidates for a refined AEDU class. Perhaps AEDU would be better recieved if it was used sparingly on certain classes that did not exist as such in earlier ediitons and they could tweak the stucture as well to take up less room. I don't think they will be able to include AEDU options for every class due to space limits in the D&DN PHB- compare it with the 4th ed PHB and how much space the 8 classes took up there (over 100 pages, D&DN is going to have 14 core classes). The Sorcerer is another class you could do as AEDU. That would give the 4th ed players 3/14 classes which consider that there is 5 versions of D&D seems about fair (1st-4th+ BECM). Its not ideal from a 4th ed payers PoV but its is better than nothing IMHO and I do not thin you are gogin to get 8 AEDU classes let alone 14 in the core rules goign by the playtest packet class design options.
If one cannot fit in some 4th ed style classes they could also have 2 PHB on release and let each group decide what version they want to use although I doubt they would do this due to confusion over what PHB to use or sell. The first 5th ed splatbook released should be focused on 4th ed players with perhaps an AEDU option for every class. Normally the 1st book released for a new edtion is a class type book focused on martial characters (Complete Fighters Handbook, Sword and Fist, Martial Power). Its probably no secret on these forums what my perosnal preference is when it comes to D&D but if I was playing a D&DN I have to admit a 4th ed inspired Warlord class doing similar things to a 4th ed warlord sound appealing even in say a Pathfinder game- PF doesn't have a warlord equivilent let alone an AEDU one.
Thats more or less it. Right now I do understand why 4th ed players are raging about D&DN. Elements of 4th ed are there but I wonder over the logic of putting a class like the Monk into a playtest packet before the Warlord. Hopefuly the next playtest packet will have 2-3 more classes in it and the races need help ASAP and that would be a good time to add the Dragonborn IMHO. It seems obvious that the 4th ed players are not getting alot but give them something at least. I'm more interested in both the Warlock and Warlord than the Monk and I suspect most 3.5/PF players do not care that much about the monk anyway (still sucks in PF),