khajiit and bosmer get bonus to sneak
redguard get bonus to stamina
breton and altmer get bonus to magicka

what playstyle are you thinking?

Yeah Argonians can stack Alchemy potion passives, with NB potion passives AND their racial . Really helps in those sticky situations. Plus they are resistant to disease and poison damage. Venom Arrow hurts less then!

-Bosmer and Khajiit by merit of racial passives can get closer to an enemy before being detected. There is gear and potentially Champion points which can mitigate this as well. Khajit also have nice bonuses to weapon damage.

-Redgards are just awesome with stamina, stamina regen, and stamina drain abilities in general. Imperials have a very high base stamina and the red diamond trait. Orcs and Dunmer have mediocre stamina boost. Dunmer also have very strong boost to magicka as well, making them potentially very interesting for both flinging magic and weapon abilities. Dunmer make great aggressive characters for this reason. This is interesting even for your blade style because a lot of nightblade abilities that enhance weapon attacks are magic based (this consideration also applies to the possibility of playing
Altmer or Breton as well)

-Argonians are thematically cool for the shadowscale style, and they get a lot more out of potions they use, particularly if they are alchemist nightblades.

I'd say its really hard to plan though. I've got this nagging suspicion that races are going to be a nice starting point for our characters, but that the Champion system will allow us to round our character out in any direction we want. That being said I'll tell you my thoughts on the issue. Considering what you want to build, I recommend you go with Bosmer, Khajiit or Redgard. The Bosmer is the same as a Khajiit but trades a boost to crit for resistance to disease and poison. From a pvp perspective I think the Bosmer is a better choice than the Khajiit. The Khajiit on the other hand has a nice little bonus to crits, which a lot of players tend to have resistance to in their enchantments. This is why I think Khajiit might be better than Bosmer for pve (although there are actually a lot of poison enemies in the game). In terms of weapon attacks, nothing beats the Redgard's passives. If you plan to focus on weapons, Redgard is a very good place to start. They have high base stamina and stamina regen, which simply helps with anything from stealth, activating weapon abilities, or the raw damage you unleash with your weapons.

As an EP sneaky ninja, you shoud go Nord. Ever heard saying "snaky as a Nord"?

My main Kotaro Atani is a Khajiit Nightblade that uses a 3pc Nightshade set, because of this he is Ultra Sneaky, I am always getting the drop on other sneaking Nightblades (that extra 2 meters of stealth makes all the difference). The only Nightblades I have to worry about getting the drop on me are other Khajiit or Bosmer's that are also wearing the same set. I would say that 9 times out of 10, I always see enemy Nightblades in stealth before they see me, unless a potion of detection or Magelight comes into play.