If this helps, Joe Dyer included All Spells! in his recent Vintage 101.
Adding Saheeli, Sublime Artificer to "The Riddler"
I believe "The Riddler" can benefit from adding one to two copies of Seheeli, Sublime Artificer for the following reasons:
After playing the deck, I found that the deck did not have a sufficient amount of creatures required to win the game in the vintage format when paired up with other agro decks. I looked at similar decks that do well with casting numerous spells in a turn and I found that Monastery Mentor worked well with Paradoxical Outcome decks as a win condition of overwhelming an opponent with Monk tokens. Though having Monastery Mentor in this deck would look good, I feel that the deck would not consistently produce enough white mana needed to cast Mentor even if additional white sources were added. Also splashing in white mana for just Mentor may not be a good idea. Adding Seheeli, Sublime Artificer to the deck would not take any alterations of mana sources. After testing this deck with Seheeli in it, I found that I had generated sufficient Servo tokens to win games against agro-heavy vintage decks.
Saheeli, Sublime Artificer's activated ability in combination with Time Vault is of great advantage. You can turn another artifact you control into an untapped copy of Time Vault and gain an extra turn with it. You can do this twice with a new Saheeli and you can even gain more than two additional turns by bouncing Saheeli with Paradoxical Outcome and replaying her. A couple of extra turns should be enough to win the game with this deck.
Saheeli, Sublime Artificer's activated and triggered ability in combination with Bolas's Citadel is an alternative win condition. Saheeli can generate a large amount of Servo tokens in this deck that can be sacrificed to Bolas's Citadel to make the opponent loose ten life. To make the opponent loose an additional ten life to win the game, use Saheeli's activated ability to copy Bolas's Citadel and use it's activated ability. There usually is enough leftover Servo tokens and other permanents available to sacrifice to the Citadel copy.
Saheeli, Sublime Artificer can be exiled to Force of will if you choose to do so.
Saheeli, Sublime Artificer can also be used to copy Hollow One on something like a Mox if needed or copy Blightsteel Colossus.
I believe that only one or two copies of Saheeli are needed since the deck has a massive amount of card draw.
Any feedback is welcome.
Not to mention the fact that it is just not a good creature for Shops decks...
Umori is always in your hand as kind of a free creature that is always available to cast. Aggro Shops always could use another creature with a decent power / Toughness that can also reduce the cost to play artifacts, very useful when you are trying to overcome Sphere taxing effects. It just takes the room of one sideboard slot.
@daniel-worobec umori conflicts with dismember. it also conflicts with boarding in leyline, but i think that's about it.
According to the link here: https://magic.wizards.com/en/articles/archive/feature/ikoria-lair-behemoths-mechanics-2020-04-02
"Your companion's deckbuilding rule applies only to your starting deck, which is the deck you begin play with each game. It won't consider any cards in your sideboard, so those cards don't have to follow the deck-building rule."
So you can put whatever you want in your sideboard and not have it the Companion requirements limit your sideboard.
Umori, the Collector in Workshops
Since most Workshop decks are all artifacts and lands you can play Umori, the Collector in your sideboard as your Companion. I know there isn't very many colored mana sources to cast it but it only takes up one side board slot and I think it would be OK to but in two Urborg, Tomb of Yawgmoth to help pay for it's cost. Also by adding Urborg in, your Ancient Tombs can produce mana without having to cost life and Mishra's Workshop can produce mana that can be used for other purposes than casting artifact spells, also good for Dismember.
Thank you Joe Dyer for interesting views on cards being banned in the vintage format.
Another aspect that cards will eventually be banned in vintage is a combination of time and the willingness to keep the game of Magic interesting. The goal of Wizards of the Coast is to keep the game going and to sell cards, these two objectives go hand in hand because selling cards generates profits to keep the game going. To keep the game interesting, new and often powerful cards are often printed every year. Lets take into consideration of what happened in 2017. Monastery Mentor made up a large percentage of the decks being played in Vintage, was then restricted and then the number of Monastery decks went down but Monastery Mentor is still one of the primary win conditions in Paradoxical Outcome decks even though being restricted. People play Time Vault and one copy of Manifold Key in their decks as win conditions as do people play Tinker and one copy of Blightsteel Colossus as win conditions; restricting Manifold Key and Blightsteel Colossus would have no effect. Now take into consideration Demonic Consultation and the new Thassa's Oracle, both win the game in combination with each other with Demonic Consultation already being restricted and only needing one Thassa's Oracle to win the game with; restricting Thassa's Oracle would do pretty much nothing. All three examples are a different way of winning the game and require different hate strategies to counter. It appears to me that Vintage in going to be dominated by one type of deck in the future where restrictions will do nothing. All you need is two of a variety of different combinations of cards to win the game. With the availability of tutors, draw spells, Serum Powder and the mulligan getting one of these three card combos into your hand is very likely along with ways to protect them, have disruption and being able to combo within the first couple of turns; and in such a deck a single Monastery Mentor will also work well. I am not sure if such a deck exists today and I also think that I am missing some combinations of cards that work well with both of them being restricted. I am however certain that as the game of Magic progresses there will be more synergies and combos made and that such a deck will dominate the format; where restricting cards will do no good and Wizards will be forced to ban cards to balance the format.
In regards to dredge decks. Is it safe to assume that you can take out Dredgers and put in some Once Upon a Time in place of those dredgers since it will find dredgers or and additional Bazaar of Baghdad? If so maybe 4x Shambling Shell, 1x Golgari Grave-Troll and 2-3 Once Upon a Time (maybe Hogaak too) may be enough to bring back Force of Vigor back to the Main Deck from the Side Board.