It doesn't synergize well, but I feel like this deck should run Elite Inquisitor for flavor reasons

The Nykthos plan is... ambitious imo. Nykthos can pretty easily ruin your opening hands and will not be consistent enough in casting 5-drops before it's too late for it to matter. Modern is a perilous place for creatures. If you want to run the Angel, just add enough lands. They can be utility lands such as Ghost Quarter, Tec Edge or WB Heights - you're running 3x Ranger of Eos anyway, so additional lands wouldn't hurt. Besides, 3x Angel is overkill by at least one.

Oh, also: not playing Ajani's Pridemage is pretty weird. It's one of the reasons to play Soul Sisters instead of a non-thematic White Weenie deck. You're paying a quite high price for Serra Ascendant by playing not-so-great cards like the Soul Sisters and Martyr.

I disagree 326 even in a non opportune setting I see few instances in which a nykthos coulnot be played by turn 3 and generate mana in excess of the initial cost due to his devotion to white and the many 1 drops he runs. This only become even more true if he decides to run Ajani's Pridemate. I however would move ghost quarters into a side board as its not necessary unless your fight a deck its meaningful against such as Tron. This gives your mana base the rigidity it needs to run Nykthos, Shrine to Nyx.

You need four points of devotion on the board for Nykthos to do anything which will not be happening all that often. Nykthos is an acceptable 1-of because of the niche uses it has with stuff like Ranger - adding more is generally just not worth it unless you're playing something like the GR Devotion deck.

Playing a soul sister deck you do not aim for a turn 3-4win because as a life gaining deck you are base around stalling your opponent by making an aggressive strategy against you more difficult. By that logic of you do not have a late game solution for victory you fail, not to mention that your biggest threat in competitive play will be affinity and tron, which white has answers for (however they slow down the deck) thus by this understanding if you don't run something like nykthos you set your self up for failure when you inevitable fight the threats that competitive will throw at you :/ but if you don't accept that, that is fine in the end all games in magic are meant to be fun and showcase the play strategy of the user.

Soul Sisters is a synergistic deck that abuses lifegain triggers and your own high life total to make cards such as Serra Ascendant and Ajani's Pridemage absurdly efficient for their mana cost. It is not a "gain life to manage to get into the late game to play random 5-drops"-deck.

"not to mention that your biggest threat in competitive play will be affinity and tron, which white has answers for (however they slow down the deck) thus by this understanding if you don't run something like nykthos you set your self up for failure when you inevitable fight the threats that competitive will throw at you :/"

Are you trying to say that running Nykthos is good in the matchups against Tron and/or Affinity because your sideboard options slow your deck down? Because that is how I understood this part. If it indeed is what you're trying to say, I really don't see an argument to be made for that. Nykthos is terrible against Tron due to sweepers and the matchup against Affinity is a simple question of drawing the hate early enough. The hate against Affinity is brutal enough to pretty much just shut it down on the spot.

@326 @ArchFline Guys, should I be moderating this debate? ;) In all seriousness though, I really appreciate the in-depth analysis going here; I've learned even more about this archetype because of you guys. You both make valid points. After extensive testing, I've ultimately decided that the deck does need another finisher like Archangel of Thune. The Archangel impacts the board dramatically and has amazing synergy. However, 20 lands was not nearly enough and didn't like Nykthos felt in the deck overall; It was kind of clunky. So, I've taken from the best of both your arguments. Anyway, thanks so much you two; I've never gotten this much input before!

Sorry Arnez but good luck with the deck, feel free to delete my comments if you like, they are just cluttering up the comment box.

Have you thought about Serra Avatar + Wall of Reverence?

Also, while this may not be of much help Grand Abolisher is a great card for protection.