I think they will follow the path taken in M20, so Elementals, Spirits, Pirates/Rogues and - I don't know - Knights? They did such thing last time if I'm not mistaken.
Someone is out of his mind unbanning Servant while cards like Ugin, the Spirit Dragon exist. Iona was just icing on a cake of banning it. Prepare for Grindstonning...
I like the idea. My Azusa is that kind of deck in part but I have "only" 50 lands and kill only with Dark Depths. Anyway to get Thrasios going you need a lot of mana so consider adding UrzaTron lands and Cloudposts. Since you will get lot of mana eventually think about using power of Eye of Ugin and Eldrazis as wincons. It will cost you only few land slots and you can even cut second Partner or change it to Vial Smasher to hit opponents twice (when the time comes).
I play Bold Impaler in my build but will replace it with Knight of the Ebon Legion as it's strictly better. Knight is also black and I play Ascendant Evincar as both pump and hinderance so Impaler sometimes loses his boldness. Universal Automaton has no abilities so is worth less than token it makes. Big NO for it. Just my three eurocents.
I reference Vilis as Bruce because of Die Hard series. You know, the more he was beaten up / injured the more effective / determined he was. Yes, that's kind of stupid
As for Yawgmoth I browsed through some decklists and most of them included a lot of useless stuff only to work with Yawg. I like playing good cards or at least ones that aren't dead draws without Commander.
MBC is my favourite archetype and I've played Sheoldred for a long time until disassembled due to being too slow for competitive meta. When Yawgmoth, Thran Physician was spoiled my hope for returning raised. Then spoilers showed Vilis, Broker of Blood and now I'm torn which one to choose.
Yawgmoth
PROS: quite cheap (4 mana), free sac outlet and removal, proliferate option. Two-card combo with Nest of Scarabs.
CONS: needs creatures to sac which forces to use token-producers and weak, self-recurring creatures. Deck may not function without it.
Vilis
PROS: draws cards off playing MBC stamples (Toxic Deluge, Snuff Out, Imp's Mischief etc.), removal of stick, big demon. Two-card combo with Necropotence, Doom Whisperer.
CONS: very expensive (8 mana), needs to focus on ramp and more on life-gain effects.
You miss few important creatures for Yawgmoth's free sac ability. I'm talking about Cathodion, Su-chi and even Myr Moonvessel. They are basicaly free dorks which can also store mana for later "big-plays".
I finally managed to play Izoni few times yesterday and have to say she's no match for competitive decks. She ramps very well after changes I made but unless I have combo pieces out I'm pretty much doing nothing. Well I was hosed badly by Grafdigger's Cage twice but anyway she doesn't pose a threat by herself and that's her biggest flaw. She's probably fine in more casual meta though.
Sadly I did not play at all for several weeks already so no news here I'm affraid. Anyway Explore creatures is good call but I will wait for a price drop to include likes of Jadelight Ranger or Doom Whisperer (kinda similar effect). Guardian Project has no place in Izoni as it doens't do anything with tokens.
I run Izoni IRL, and she's been giving me great results with a list similar to yours. Compared to you, I focus more on loading the grave quickly, by relying on abilities like Explore and Dredge. Life From the Loam is an exceptional card on this regard, as it keeps loading your grave with stuff and your hand with lands, which should solve the mana issue. Stitcher's Supplier has also proved to be exceptional for me. Losing combo pieces in the process hasn't been a problem thanks to cards like Seasons Past, Eternal Witness, and the new 4 mana Golgari creature that retrieves permanents froma grave.
A card I've been considering lately is Emrakul, the Promised End. I mean she's capable of having a huge impact on any game, and she likes a loaded grave and mana ramp, two things a Golgari deck should easily be able to provide.
I also value redundancy more than you: rather than running three combos, I run one combo, but with each piece having two or three potential replacements.
Which single combo do you run? Infi tokens?
I dislike cards that force me to bin cards I'd like to have in hand. Stitcher's Supplier may cause to mill crucial combo piece or important spell and Izoni herself do not let me get it back. I used such cards while playing Sidisi but even there they were equally annoying as they were helpful. I'd rather go more into cycling than random mill. Explore cards may work though.
Also - do not underestimate power of Panglacial Wurm
As for Yawgmoth I browsed through some decklists and most of them included a lot of useless stuff only to work with Yawg. I like playing good cards or at least ones that aren't dead draws without Commander.
As for landfall effects Amulet of Vigor works very well with any taplands. Add Exploration / Burgeoning / Azusa and reap even more benefits from Karoo lands.
EDIT: Somebody needs to break Embodiment of Insight with Yarok.
Yawgmoth
PROS: quite cheap (4 mana), free sac outlet and removal, proliferate option. Two-card combo with Nest of Scarabs.
CONS: needs creatures to sac which forces to use token-producers and weak, self-recurring creatures. Deck may not function without it.
Vilis
PROS: draws cards off playing MBC stamples (Toxic Deluge, Snuff Out, Imp's Mischief etc.), removal of stick, big demon. Two-card combo with Necropotence, Doom Whisperer.
CONS: very expensive (8 mana), needs to focus on ramp and more on life-gain effects.
Have you noticed shape of her upper wings? They're like Bolas' horns...
Guardian Project has no place in Izoni as it doens't do anything with tokens.
EDIT: Since you're using Archaeomancer and Mnemonic Wall, Ghostly Flicker could work well with one of the mentioned and Peregrine Drake / Palinchron.
Which single combo do you run? Infi tokens?
I dislike cards that force me to bin cards I'd like to have in hand. Stitcher's Supplier may cause to mill crucial combo piece or important spell and Izoni herself do not let me get it back. I used such cards while playing Sidisi but even there they were equally annoying as they were helpful. I'd rather go more into cycling than random mill. Explore cards may work though.