To be a realist here, I have to agree with TailsAlone that the writers probably won't implement such a thing into a TV show like this, as interesting as it is. Villains are created through vices being their cardinal traits, their behaviour directly stemming off from committing actions according to their sins, and thus it wouldn't be insane to think such a thing would apply here. That said, So far, the three villains have captured some of the vices pretty well. Let's take a look.
Nightmare Moon: Envy. Princess Luna transformed into Nightmare Moon because she was envious of her sister's ability and slightly higher status among ponykind. Somehow, I get the feeling that Luna not only wanted her night to be appreciated much more than just looked upon, but also sort of yearning to have the effect that Celestia's day puts upon her subjects. Eventually, of course, she went over the edge and transformed into something pretty wicked, even though it was emotionally charged and wasn't pure evil, she was subjected to it quite easily.
Chrysalis: Lust. Let's face it, she not only wants to feed her minions by sapping the love away from Equestria's denizens, but she also wants Equestria all for herself. The fact that she went out of her way to sing an opera about it, about how she's a fake and doesn't care for Shining Armor at all speaks a lot about her character. There is an intense look in her eyes every time you see them - nothing but an intense desire to rule over all of Equestria. And do not be mistake - lust goes beyond just excessive sexual wants. It can apply for power as well as fame or wealth.
Discord: Pride. This guy is a cruel prankster and joker, and he knows it. He reminds you of the hooligan down your street who pulls mean pranks on you just to make himself feel better, and that's really all that he is. That doesn't stop there, however. As a viewer, you were subjected to his various taunts that were directed to not only Twilight and her friends, but also Princess Celestia and her kingdom. He was so confident in his "jokes", however, that he became very arrogant throughout the season two premiere which led to his eventual defeat. He's also given us the impression that he cares for no one other than himself and his work... which wreaked havoc in Ponyville.
Celestia's simile of his heart being "as black as night" seems to speak great volumes in itself - I definitely got the same impression as you did. We have not seen a ruthless and homicidal villain yet, and his antics will surely have a unique impact on the Mane 6.
Of course, wrath stems from rage - if Sombra is revealed to be angry most of the time, we could be headed somewhere with all this.
Oh, I almost forgot - if you remember, I made a thread back in May (I think) which spoke about how the major villains represent the opposite of each Element of Harmony. For example, Discord was Pinkie Pie's antihesis (to put it into perspective) because his kind of sparking laughter was vile and pretty mean. It wasn't fun at all. Likewise, Chrysalis rose to power through lies and deception not unlike Emperor Palpatine from Star Wars - the complete opposite of Applejack. And Nightmare Moon was driven by a selfish desire to reign supreme over all beings and to command them, not really caring for them at all - the opposite to Twilight Sparkle. If we follow that line of thinking, and given Sombra's character, he could turn out to be the opposite of Fluttershy's Element of Kindness as, once again, his heart is as black as the night.