This is not going to end well.
Anyway balance in RPG's (not just D&D) is subjective and it is shaped by the genres and individuals expectations. It also varies by the game world the DM has created and the amount of combat and non combat expected. Perfect balance is a waste of time IMHO due to these factors and even then there are other ways to deal with it.
Recently on the forums there has been a few arguments over stat generation ability, basically point buy vs stat array vs rolled. I generally let my players use whatever one they like but I warn them don't bother overly min maxing point buy as it will bite you in the ass (7/7/7/14/16/18 etc). Most of my group picks stat array or point buy one of my players prefers to roll and so do I. If we roll up a weak character we just min max harder or take a more powerful race or class. A pre 4th ed Drow for example with full NPC drow racial abilities isn't such a huge problem if a PC rolled a 12 as their highest score.
Not that we actually play Drow (well ok we done a Drow campaign once) but its easier to identify something like that than one of my home brew races. Put simply we balance things out ourselves if we want a high powered game everyone can be Drow and use 10,12, 13, 14,14,16 stat array. Our gaming style will not suit everyone of course. I actually switch it up. One game will be anything goes, another game will be a lot more restrictive. Currently in my 3.XYZ mish mash game one cannot even take levels in a spell caster class until level 3 due to a systematic purge of magic over 1000 years.
However balance can also be genre related. In the old WEG D6 system if your opposed strength roll was exceeded by 16 your character was killed. 3D was a reasonable strength score, a sniper rifle dealt 7D damage but a head shot added +2D damage and character points could add another 2D and bring that to 11D6 which was opposed by a 3d6 strength roll. An average damage roll from a sniper rifle will kill your PC with no saving throw allowed. That may be unbalanced from a D&D point of view but what if you are doing a gritty game set in real life and your PC is a soldier charging up Omaha beach? Change the genre again to a James Bond themed game and you can use the same mechanics and add some sort of destiny/fate/action/force/luck point resource that can mitigate that instant kill shot (bad guys can't aim in movies anyway and that's why).
An orc fighter with a great axe can be a scary thought for a level 1 PC. A 3.5 raging orc level 1 barbarian can one shot a level 1 PC maybe even to negative 10 hit points. I am fine with that if that's what people like. Personally I would very rarely use an Orc Barbarian like that and if I did I would probably tell my players “this is a gritty and deadly campaign” or words to that effect. 3.5 and 4th ed had there various problems but once again balance is subjective. Some 3.5 gamers probably liked that others may not have but still liked the system overall. Same thing with 4th ed players they may not like certain aspects of it but they will still like the system overall. You cannot really balance what people want or what they will be happy with.
In core rules it is usually easier to add something than to put something in and take it out later. Anything that is drastically different is better off in a splat book or campaign setting. Races like Warforged and Eladrin can cause problems by their very existence depending on the tone of the DMs world. Inherently magical/monstrous/supernatural races will not work in some worlds. A Warforged fighter is a no go if the DM has a plot hook involving a long lost parent/sibling/claim to the throne event for one of the PCs. An Eladrin cannot be imprisoned in a conventional Earth prison/tower, a Dragonborn bar fight could easily kill the mundane races despite being balanced in combat mechanically with other heroes. Some DMs could ban them for that reason. Some of the historical themed source books from TSR went as far as banning all non human races and the wizard class and nerfing the cleric. Once again that's fine but it is better off in a source book. If you don't like it don't play that setting or buy that book. An Elf let alone a Warforged does not belong in a Rome themed game. A fantasy Rome however could have the huns be an Orc horde, the Pope could have a half elf child.
I don't think Mearls and co are sitting around in an office cackling about how they can screw you over personally but it is impossible to cater to everyone tastes on the release of D&DN despite it being inclusive as a design goal. I'm not going to get to upset if they include a Dragonborn and exclude a Warforged (vice versa maybe). This is where I think the module part is going to come into play. It just depends on what people expect on release. It was unfair to 4th ed to expect it to match the splat book bloat of 3.5 on release and it is unfair to expect everything from D&DN on release. If you have impossible expectations of course D&DN will suck. I'm still waiting for my Spelljammer update dammit;) Some things are just going to be fundamentally incompatible with your expectations at least on release.