I've been playing this archetype a lot over the past two weeks, and it has potential as an anti-Shops weapon at least until Workshop, Ballista, Tangle Wire, or Sphere gets restricted in a few months. I went 3-2 in non-mirrors in the P9, but have also cashed my last six daily events. The deck has very good matchups across the format. Being pre-boarded for Oath and Dredge, the two decks people most like to play to try to pick on Shops, is just ridiculous.
Play 4 Thalia, Heretic Cathar. She is great in every single matchup. She creates free wins against Shops and Eldrazi if you have her early enough. I have beaten Dredge with her, the smaller Thalia (Smalia), a Wasteland and no other hate. She is great against Paradoxical Outcome because often their only out is topdecking Tolarian Academy. If I had a dime for every Mentor pilot who has wasted their turn trying to flash in a Containment Priest to ambush something I'd have enough to buy a fifth Thalia, and she's like a $4 card! Steve's dismissal of her is ignorant; she's probably the best creature in the deck. I don't trust the judgment of pilots playing fewer than 3.
Play 4 Thalia, Guardian of Thraben. This is obvious but for some reason people keep playing 3. I like that not everyone plays 4 because it makes it really quick to figure whose lists to ignore.
Play 0 Thought-Knot Seer. The card is weak in your close matchups and unnecessary in your good ones. Cutting this improves every other card in your deck. Your Wastelands get better. Your Thalias get better when you can actually use your Wastelands. Your Reality Smashers get better when you cast them instead of letting them sit in hand. Your Displacers get better because less often does activating them mean a TKS is rotting in your hand. Your mulligans get better. You get to cut some temples for Flagstones, which makes your sideboard options a lot better. Crutching on Temples to cast your mediocre Thought-Knots ripples through your sideboard. By cutting this vanilla 4/4, you improve like 30 cards in your 75.
Play 0 Vryn Wingmare. Three mana for an X/1 is embarrassing against Ballista. This card isn't garbage but usually people who play it are replacing some number of Thalias, which is incorrect. Your worst matchup is Shops. If you build with that in mind, it's at least 50/50, so build with that in mind.
Play 0 Lodestone Golem. This card probably shouldn't even be played in Shops right now.
Play 2-3 Mental Missteps in the board. You don't need redundant Thorns affects. They are marginal against combo because you don't have time to play them all. Misstep is actually good on the draw. It's a blowout against anyone trying to play Swords to Plowshares. This was the lone suggestion of mine Steve actually took, and his matches in VSL illustrated how great a sideboard tactic Misstep is against Gush decks.
Mulligan aggressively. Very rarely keep hands that don't have a turn one play. Use the scry rule.
Eldrazi Displacer is good (and probably correct right now) but not an automatic include. I have played lots of similar, reasonable board-affecting cards. Stoneforge Mystic, Smuggler's Copter, Fairgrounds Warden, Gisela, the Broken Blade, Linvala, Keeper of Silence, Archangel Avacyn, Toolcraft Exemplar, Ranger of Eos, Walking Ballista, Hero of Bladehold… there are a lot of rares and mythics you could play.
I turned off the Copter after Ballista came online because of how much removal rational blue players should have for their Shops matchup. Additionally, having an empty vehicle in the face of Ballista isn't a great feeling either.
The core of the deck is so strong it's hard to tell which auxiliary cards are better or worse. It's easy to play the deck, even get good results with it, and have no clue about where your wins are coming from. You have to be pretty honest with yourself and detail-oriented to evaluate what is actually good. You can't be results oriented because even good results are misleading. This is what leads people to continue playing 3 Thalia or Wingmare or Thought-Knot Seer. I've played:
4 Copter, 4 TKS (gave it a second chance to rule it out definitively)
4 Fairgrounds Warden, 2 Gisela, 0 TKS
2 Fairgrounds, 2 Gisela, 4 Copter, 0 TKS
4 Displacer, 4 Copter, 0 TKS
4 Displacer, 2 Fairgrounds, 2 Gisela, 0 TKS
4 Displacer, 2 Fairgrounds, 2 Linvala, 0 TKS
4 Displacer, 1 Fairgrounds, 1 Gisela, 2 Linvala, 0 TKS
What you should take away from that sample is that the core of the deck is so strong that a lot of your other creatures end up being marginal. Displacer is probably correct at the moment because of Shops, but even then, playing 4 Fairgrounds Warden and Linvala/Gisela also seems fine in that matchup.
This deck has an absurd number of matchups that are just close to byes, and it's lone "bad" matchup isn't even that bad. It's the best deck I've played since Rally the Ancestors was in Standard. Contrary to Steve, I think it's a pretty easy deck to play, and I don't doubt its pilots get an edge from lack of mental fatigue.