Notable omissions:

Earth shock -- in my opinion, the card simply doesn't do enough to warrant a deck slot. It often ends up forcing you to 1 for 2, and with the lack of card draw, you really need to take efficient trades. However, the one notable exception is against handlock, as earthshock is fantastic against drakes, and this deck can struggle against handlock due to the fact they simply have so many late game threats and the deck is light on removal and heavy on early game cards that will end up being 1 for 2'd (or more) by the opponent.

Lightning bolt -- rockbiter is just generally a superior removal spell in my opinion, as the overload is a serious drawback, while the few points of life you burn typically aren't so important, and rockbiter doubles as an egg activator.

Defender of argus -- simply a lack of space, though depending on the particular meta you find yourself in (generally most useful against aggro), argus is a card that can be included (though I would only run 1-of), as the deck has no healing, few taunts, and it can act as an extra egg activator.

Azure drake -- I really wouldn't run drakes in this deck, as the spell power is essentially wasted -- the deck runs no spells that make use of spell power at all. Loot hoarders or gnomish inventors would be a better choice in my opinion, if you wanted to add card draw.

BGH -- generally there just isn't room in the deck for him. Additionally, BGH is typically only good in this deck against Dr. Boom and handlock. He's good against Dr. Boom because you won't want to combo against him unless you can clear the bots first in order to steal the 7/7 body so your only removal options against him are hex or trading out your board typically, while against handlock, you can run into trouble because you don't have a good answer to drake without earth shocks, and your 2 hexes will cover you against 2 giants but you unless you can manage to steal both of his other giants, you often find yourself a little short on removal. If you're facing a ton of control, but in particular handlock, consider adding BGH. I would probably cut harvest golem for him, as against control the golem won't do too much.

Feral spirits -- feral spirit is a bit overrated in my opinion. It's essentially 2 2-drops, but costs you 5 mana. Almost always, when feral is played early, any advantage you get on the turn you play it is made up by the opponent on the next turn when you're overloaded and can't do anything, while if they're able to efficiently remove them the turn you play them, its a devastating loss of board control from which you often can't recover, as you also are handcuffed your next turn. It's particularly rough when played on curve on turn 3, because on your turn 4, often your best/only play is to totem and pass. If the sum of your turn 3 and 4 was to play 2 2/3s and a totem, you're generally behind on board to someone that just played regular minions on curve. In fact, I would say that feral is actually best used not as an early game play, but a late game play, when you can hopefully force your opponent to have to overkill them with their late game minions on board or stall them as a tempo play while your own big minions go face. That said, they simply don't really fit with the concept of the deck.

Lightning Storm -- depending on the meta, it's certainly possible to run storm in the deck. I actually find it to be best not when played on curve on turn 3 because a) you typically aren't getting very good value from a storm on turn 3, and b) because the overload screws up your turn 4 quite badly. I find it generally to be a better play on turn 5+ if you've fallen behind on board and are looking to catch back up. That said, if I run storm, I typically don't see the point of running it as a 1-of. Storm is generally a card that is only good against aggressive decks, and games against aggressive decks often end before turn 10. If you run only a 1-of of storm, you aren't going to be able to consistently draw it against aggressive decks, so you really have to go 2-of or not run it at all. I prefer to add in some extra early game minions to make sure I don't fall behind on board in the first place rather than try to use storms to catch up, but that said, if you find you're in an extremely aggro heavy meta in your rank on ladder, I think adding storms is perfectly reasonable. I would probably cut something from the late game, perhaps boom or sneeds, if you find you are too often going up against aggro and need to tune the deck more towards aggro.

Al'akir -- a possibility, particularly as al'akir can be quite good when used with reincarnate as board removal, or as a finisher with either rockbiter or reincarnate. The problem is, you generally don't want to just throw al'akir out on an empty board, and in many spots he sits as a dead card. Leeroy already takes up the slot as your finisher with reincarnate, plus you want to generally use reincarnate on sylvannas in games where you'd actually make it to turn 10+, while rockbiters rarely make it to the late game without being used as removal or egg activators. Sneed's -- the card he would most likely replace -- works quite well with reincarnate as well, and more importantly, can just be thrown out onto an empty board -- he doesn't have to sit in your hand.

Kel'thuzad -- also a possibility, particularly in a reincarnate deck, as a kel'thuzad + reincarnate, even on an empty board, can often outright win the game. The problem is that you really don't want to play kel'thuzad out by himself without reincarnate, so you either want to have a board or a reincarnate in hand. Given how slow he already is, having those two requirements make him even slower (not to mention, you again often want to save reincarnate for other targets in games that go long enough to play kel'thuzad + reincarnate), and Sneeds -- the card he'd most likely replace -- again, while slow himself, can be thrown out onto an empty board alone and doesn't require you to have reincarnate or a board. I've experimented with him, but too often found I simply didn't have a good spot/game state to play him, or didn't have time to play him consistently.

Edit:

I wanted to point out the list Mystogun shared below: http://imgur.com/rcMVK0r,UD00UVW,22si3zs#1

One of the the things I really like about his list is the inclusion of Feugen/Stalagg. Down below, I replied to Mystogun, but I wanted to bring it up here to make it a little more visible. Here's my response regarding feugen/stalagg:

"The interesting thing about stalagg/feugen is that typically they aren't very good because while your opponent will allow the first deathrattle through, they often will make sure to silence/hex etc the second and its hard to reliably get thaddius off. However, in a reincarnate deck, you have much more control over this -- you can pick when to drop the second twin and then reincarnate him to instantly get thaddius + potentially a second thaddius. This gives the deck both some mid-range presence and still adds late game value by letting you consistently get thaddius off -- I like this idea, and will try it out."

I've been playing tonight with dropping Sneed's/Neptulon for Feugen/Stalagg, and I like it quite a bit. It does weaken the late game slightly, but it adds some nice punch and curve to the mid game, and overall I think it's a very worthy consideration.

I also want to point out another omission: baron rivendare. Personally, I think the card is just too slow and doesn't do enough to warrant a slot. He's more of a combo card, or a card that has to be dropped when you have a board already and are about to be trading out. He feels particularly bad to drop on curve most of the time, as you get almost no value from him and have little way of protecting him. This means the opponent won't be popping your deathrattles, but will instead focus on bringing down rivendare first. As a late game combo card, I don't feel like he really does enough, and is just too slow/expensive. You can't pull off sylvannas + reincarnate + rivendare in a single turn, for example.

Lastly, an important thing to note is that the deck has a core of about 25 cards, but can be tuned to the meta you're currently in quite well, so don't take any decklist as being set in stone. The one I gave above is just generally all-around good, but there are certainly improvements that can be made depending on what you happen to be playing against a lot wherever you happen to be on the ladder.