...Having 9 basics has been a huge advantage thusfar due to the popularity of crucible ... big enough I think to outweighs the advantage of the extra color.
Answered the question I was just about to ask.
So crucible is the only reason keeping this deck from adding a little support...
But could the help of say White, or Blue even outweigh the setback of 1 card?
Well the "Standard" nethervoid is supposed to play green for artifact/enchanment hate and pernicious deeds instead of powder keg (although to be honest I've found powder keg to be better/faster and do almost everything I need anyhow). I just didn't see green being useful enough.
White is an interesting idea, I mean moat or wrath would help this deck immensely as it has creature problems to begin with, and resolving an armageddon with a nethervoid and a weenie in play would definitely give you an insta-win ... but with the void in play you have no excuse to lose anyhow. White I hadn't considered much.
Blue, on the otherhand, is worth thinking about. I mean what deck can't use a timewalk and an ancestral? There is also a lot of synergy with standstill with this deck (look at all of the utility-lands). Nethervoid is a rather successful deck simply relying on top-deck glory, so give it some card acceleration and you should be guaranteed a win. Also lim-dul's vault is a highly underrated card that any deck would love to play and mana leak is viable in a splash. I would have to seriously rework the deck to work in serious blue disruption of any kind (mana drain, FoW), but just splashing blue is viable I feel ... again at the cost of land security.
So I am probably going to toy with blue here ... which as far as I know is rather unprecedented for nethervoid. I'm hopeful it can make the deck competitive tier 1 ... but I honestly don't know.