It's definitely an option that's worth exploring.
Workshop does have a couple of advantages over City of Traitors, but I'll admit that it's unclear how valuable these advantages are in the present style of builds.
Perhaps the most important advantage of Workshop is the ability to cast lockpieces on consecutive turns while letting Bazaar do its thing. For example, you can cast Sphere on turn 1, then Sphere on turn 2, and play Bazaar. That gets both plans online immediately, whereas City of Traitors would require a second, suicidal land drop.
The other advantage of Workshop is that it stays around longer. Keeping the land count high on the battlefield can be important to leap over the deck's own taxing effects. Cards like Sphere and Loam get harder to cast in the longer games. So long as Workshop has an enabler like Urborg or Riftstone Portal, it can help support any part of the game plan.
All that being said, Workshops and City of Traitors aren't mutually-exclusive. It's possible that some number of each is a viable approach, or that the latter belongs in the sideboard.
As a final comment, although the deck features Stage/Depths, I generally don't try to "turbo" it out as is common with traditional dredge lists. I rarely keep hands that have Stage, Depths, and Tomb with no other gas--it's just too slow. Even in those cases where I have disruption and the Marit Lage triplet, I often prioritize the mana denial plan (Wastes/ Loams etc.) until I can make sure I can swing in without worrying about Swords, Repeal, etc. The real value of Stage/Depths, in my eyes, is that it increases the range of acceptable hands--you get to be more picky when you can win with the Dredge part, Marit Lage, or Hollow Ones, each of which have different enablers.
Snagged a 5-0 yesterday with this list:
The older style lists were performing well until Modern Horizons hit and dredge became ubiquitous. The first problem was that Force of Vigor severely weakened the previous plan of attack against Dredge. Leyline simply didn't buy enough time on its own to get Marit Lage on the table. The second problem was that graveyard hate became so rampant. This didn't only harm the dredge portion of the deck, but also the Marit Lage plan that leaned so heavily on Riftstone Portal and Life from the Loam.
To address these problems, I moved the Leylines into the maindeck and went with a full suite of Wastes/Strip. Even with Force of Vigor present, those Wastelands can buy a ton of time against Dredge. And of course, they don't always have Force of Vigor, so having Leylines in all three games helps. The maindeck Leylines are also great against Dreadhorde Xerox and Wrenn-and-Six decks.
I also doubled-down on the Marit Lage plan, since it can completely evade graveyard hate and cards like Swords/Repeal are fairly absent from the meta. Going back to the classic Vampire Hexmage and Urborg plan has been doing very well in post-board games.
Edit: followed right up with a 4-1 today
I lost to this. I was on the BUG list that won the challenge. Game 1 I lost and should lose to the dredge plan.
I feel like he got a little lucky in game 2. He had bazaar, lotus, thespian stage, dark depths. I had to respect the Bazaar by naming it with Needle. But the Lotus-Thespian Stage-Dark Depths was just too fast for double 5/6 Goyf beats.
The ability to stretch the opponent in multiple directions is very good, though I suspect there is some degree to inconsistency.
Depths/Stage definitely has some variance to it, both in terms of whether you assemble the combo in a timely manner as well as whether the opponent has the best answers. The metagame presence of good answers, as well as the overall speed of the metagame are major factors in determining whether Stage/Depths is a good option.
However, most decks rely on mulligans to find graveyard hate, and Bazaar can be used to dig for the combo, so Stage/Depths is a much more attractive sideboard plan for Dredge than it might be in a more dedicated deck like Dark Times. It can be a "bad" option in terms of metagame and still score quite well simply because it is hard for opponents to answer disruption, dredge, and depths all consistently.
Hogaak is phenomenal. It addresses some serious weaknesses with the deck that I'd struggled to manage before. Most importantly, it offers a way to crash through an opponent's defenses when they manage to get an appreciable number of blockers on the board, like Pyromancer tokens. This has come up enough that I've even tried running Glory or Filth to get the appropriate evasion, but those cards require a lot of work to get online (but I must say, using Glory is a blast). Less importantly, Hogaak actually provides a way for the deck to buy time against Blightsteel Colossus, which was almost impossible to deal with before.
Hogaak is also certainly worth playing in multiples, but I think playing more than one depends on the metagame. It can make the dredge half of the deck way better, and I did try versions that played 3 to 4. But I think space is tighter than usual right now and that metagame has really encouraged minimizing the Dredge plan.
As for Mana Crypt, I go back and forth. I think my decision to omit it was primarily meta-dependent, actually. I do love Mana Crypt in Game 1, where it has effectively no drawback since we're pretty fast. And I sometimes love it in Game 2 and 3 for those quick Stage/Marit Lages. But there are a few things in the meta that have pushed me away from it: first, decks are really pressuring the life-total right now--not just the obvious culprits like Eldrazi, Shops, Survival, and Dredge, but there are also plenty of Tarmogoyfs and Dreadhordes throwing bolts at your face. The damage has mattered a lot when I've tested it--and I was playing it in pretty much every list again until a few days ago. Second, I rarely sideboard Null Rod out anymore, making the Crypt a blank too often. Third and finally, since PO/Combo have dropped off, getting a turn-1 lockpiece has been less important.
Yeah, I absolutely got very lucky there. And really, I got pretty lucky in the first game, too. Variance was much kinder to me than usual.
I 5-0'd twice last week. It would have been three times had I not been inattentive and punted a lethal attack (opponent couldn't empty hand with Ensnaring Bridge in play and I missed it). I also 4-1'd four times. Overall, I've gone 35-10 with this specific list:
I know the deck can seem like a pile of nonsense at first glance (perhaps for many more glances after that).
I plan to write a primer to explain the deck once I've tracked the critical details of at least 100 matches across the various recent lists (e.g., die-roll, match-up, hand size, lockpiece on turn 1, Bazaarless hands etc.). I've played more than that already, but I had not been diligent enough with the tracking to give a full picture.
Played the above list to a middling 4-3 at the NYSE.
I won against the best match ups (Xerox, Dredge), lost two of my three medium match-ups (Karn Shops, BUG, Doomsday), and lost against the horrifying nightmare match-up (Dark Times with Crop Rotation into Bojuka Bog main deck. Quite rude if you ask me.):
Karn Shops: 1-2
Xerox (URW): 2-0
Big-blue BUG (Brian Kelly contraption): 1-2
Xerox (URW): 2-0
Dark Times: 0-2
Overall, I'm not too displeased with how the deck performed, as I only lost one more match than I would expect given performance in the leagues (around a 70% win-rate, which on average should result in a 4.90-2 record in 7 matches). I suppose that's to say that the result was below-par by one match.
I certainly made some questionable mulligan decisions in two of the match-ups I lost, especially when deciding which cards to bottom. The silver lining is that those skill-testing decisions were made possible by the London mulligan, which I otherwise detest for Vintage.
As a side note, four of my seven opponents knew exactly what I was on due to frequent run-ins in the leagues, so there was little surprise value to reap. Vintage is a small world.