i've goldfished with your list a little bit and it runs surprisingly smooth considering it has a very low land count and has 8 pox effects..
i agree with cutting 1 darkblast, 3 seems a bit too many..

i'm not sure why you have kaervek's spite in there, i'm not saying it won't work but it seems too situatonal..if you're looking for a fireblast effect in black you might wanna look at soul spike..but still, i think there are other more viable options..

since you're thinking of incorporating tha rack in your deck, may i suggest raven's crime and funeral charm, raven's crime is good since you're considering of adding another dakmore salvage, just be careful because having too many lands that CIPT might hurt your tempo ....these are very good since you're thinking of removing the dark rituals and these discard spells are cheap..i'm sure you're already aware that removing the rituals sacrifices explosiveness for consistency..

i totally agree with the inquisition of kozilek, there are never useless..about the only thing they can't hit are jace and FOW..

i'm interested to hear about your thoughts on arena after you've playtested with them..i tried incorporating them in my deck but they seem meh..
seems like pox decks(or most legacy decks) are built to run on very few mana that card draw seems awkward..i think thats the reason why there are very few card draw in legacy outside of BOB ..remember that brainstorm, ponder, etc are not card draw; they're card selection spells..anyway, off topic..

please pardon my english, i aint a native english speaker..