I am trying W6 in Chubby's Jund, and it is feeling fantastic as a mana denial. Combined with Ouphe and FoV, Green could be the new blue (a bit of an exaggeration lol). Now, I can just imagine little Chandra (M20) and W6 wrecking the world.

3 Bloodstained Mire
2 Verdant Catacombs
2 Wooded Foothills
3 Badlands
2 Bayou
2 Taiga
1 Strip Mine
4 Wasteland
1 Black Lotus
1 Mox Jet
1 Mox Ruby
1 Mox Emerald
4 Deathrite Shaman
4 Dark Confidant
4 Tarmogoyf
1 Collector Ouphe
1 Ramunap Excavator
2 Chandra, Torch of Defiance
1 Wrenn and Six
2 Pyroblast
4 Mental Misstep
3 Lightning Bolt
3 Assassin's Trophy
1 Demonic Tutor
1 Sylvan Library
1 Green Sun's Zenith
3 Thoughtseize
2 Cindervines

SB
4 Tormod's Crypt
1 Pithing Needle
1 Yixlid Jailer
1 Collector Ouphe
2 Infernal Reckoning
2 Natural State
2 Force of Vigor
1 Pyroblast
1 Plague Engineer

I don´t have the cards to test, but I think Chubby's "4c Zenith Value" list can do something against Karn if we update it with Ouphe/Gaddock. And we can rethink Humans and Survival too.

Can we dream of merfolks or goblins (with cratermaker) in vintage?

Just pointing one thing: Narset interaction with "draw 7" spells is crazy. Even pairing her with Dack can disrupt your opponent's hand.
I was about to invest some money in Mox Opal to build a PO deck, but seeing how the format is becoming a Narset x Karn war, I don´t think PO will stand a chance. A crazy mind should put both in the same list and break everything

Wow, I was trying a Karndrazi build after reading an article about it in Modern. My initial list was similar to @diophan's. But now I am trying a bolder approach and I'm having an insane win rate. Basically, it is a "non-tax" beatdown list. Just wanted to share it:

4 Cavern of Souls
4 Eldrazi Temple
4 Ancient Tomb
2 Eye of Ugin
1 City of Traitors
1 Tolarian Academy
1 Urborg, Tomb of Yawgmoth
4 Wasteland
1 Strip Mine
1 Black Lotus
1 Mox Emerald
1 Mox Jet
1 Mox Pearl
1 Mox Ruby
1 Mox Sapphire
1 Sol Ring
1 Mana Crypt
1 Mana Vault
1 Grim Monolith
4 Eldrazi Mimic
4 Endless One
4 Thought-Knot Seer
4 Reality Smasher
3 Phyrexian Metamorph
1 Endbringer
2 Dismember
1 Thorn of Amethyst
1 Chalice of the Void
4 Karn, the Great Creator

2 Grafdigger's Cage
1 Mycosynth Lattice
1 Phyrexian Metamorph
2 Tormod's Crypt
1 Trinisphere
1 Phyrexian Dreadnought
1 Witchbane Orb
1 Voltaic Key
1 Time Vault
1 Pithing Needle
1 Crucible of Worlds
1 Umezawa's Jitte
1 Walking Ballista

Edit: Sideboard

This is probably the best PW since Dack: shuts down PO, digs deeper than JtMS for 2 turns, FoW friendly, easy to cast with Black Lotus, slows down Bazaar and Xerox...