I've personally had good success with Hixus, although I can see the possible appeal of Tragic Arrogance in that slot instead. I have rarely run into a situation where I needed to use another board wipe with Hixus still on the board and him holding other creatures in exile. He can be flashed in as a 4/4 even if there are no opposing attackers to exile and he does help fuel the single Nullifier, although getting 2 cards in exile isn't too much of a problem other ways.
Plus, he's a one-sided board wipe. He hits the other player's attacking creatures but doesn't remove any creatures that you may already have on the board. This is a benefit in some ways over Planar Outburst or Languish (although many of the threats in this deck can dodge one or both of those already).
I have made the following tweaks since the original post
-1
Necromantic Summons-1
Coastal Discovery-2
Inspiration+3
Telling Time+1
Archangel of TithesCurrently sitting at around rank 20, but I have lost some games tinkering with other decks. I''ve only lost a handful with this one so far, a couple due to mana screw (including one game where I had 3 lands in my starting hand and then never drew a 4th despite holding out against an aggro deck for 12 turns) and one deck to a ramp deck that resolved Ulamog against me. Was seeing a lot of Boros aggro and RDW at the lower ranks. Starting to see a lot more green ramp decks and elf decks now.
We will see how this holds together at the mid ranks against more focused decks with more unlocked cards. It seems to have no problem with aggro decks (which are still super slow with BFZs card pool) and hopefully it will continue to fare okay against more midrange decks.