As far as Critical mass, I am referring to the Critical mass of available spell combo enablers: Memory Jar, Bolas's Citadel, Necropotence, Yawgmoth's Bargain, Oath of Druids, Gifts Ungiven, Paradoxical Outcome, Dark Petition, Burning Wish, Wheel of fortune, Timetwister, Tinker, Windfall, Yawgmoth's Will, Mind's Desire, ...
Draw7s are effectively almost as artifact mana reliant as Paradoxical outcome if you want to cast them in the first two turns and/or be able to consistently win the game after resolving one. If neither of those are part of your goals, then that begs to ask the question "why would you want to play those cards in the first place?".
But, doesn't the fact that you have to set it up make it worse than a card like timetwister?
I am not referring to the riddlesmith list, which I think completely offsets the drawback of the card and actually benefits from it. However, it remains to be seen whether that deck can outperform current combo decks.
I was thinking more along the lines of our established spell combo decks like DPS and PO, where this card is rarely going to be good and which would render those decks worse overall if you had to find room to add this card and a discard outlet.
At prima facie, this card does not belong in a Bazaar deck or a deck that would play Dack Fayden, which are the most obvious discard outlets in the format. So you would have to find another outlet which has synergies with a deck that would want access to the draw 7 effect. Riddlesmith seems like a good fit here, but I have not played with or against it.
I'm basically bringing up some of the arguments found in this article.
Given that it isn't good enough to build around in legacy, where the available combo enablers are much worse and where you have access to 4LED (which pairs divinely with this card), I have a hard time seeing this as relevant enough in vintage, objectively.
I will definitely acknowledge that this card has some very strong and unique qualities (First card of it's kind which makes it hard to assess, opens design space, increases threat density by having the potential to be a 2 for 1 against counterspells, the effect is very powerful, doubles as disruption against Bazaar decks)
But in the end, Echo of Eons seems too constraining for me to envision as viable (at least theoretically) and seems to suffer from the same issues that a card like Day's Undoing does (albeit less restrictively so).
I do hope I am wrong though because this card is definitely sweet and fun. I have full faith that if this card is breakable, Chubbyrain will find a way to build the deck that does so.
Why would you want to play this card over the plethora of alternatives that are all more broken and more practical?
What does this card enable that you couldn't do before that is better than what the current combo decks are doing?
I have a hard time buying that you end up ahead vs a control deck by putting 6 mana into this card (which can be pyroblasted or flusterstormed) to get it countered and recasting it on the following turn. Or even that this is a frequent enough occurrence to be reliable.
Another thing this does is that even when not big, it still functions as a removal spell or a tempo play.
I could see this in the sideboard of a combo deck where it either provides an alternate win-con in the face of hate or it buys you enough time to stitch together a win.
It's hard to evaluate how reliable this card is though, which will ultimately be the deciding factor on whether this is actually playable.
This is not good in vintage, might have been worth it with 4 probe legal before Dark Petition was printed but even then you already have access to 3 topdeck tutors which almost no decks play right now.
On another note, curious to see how this would play out in legacy with 12 cantrips or even modern.
This could have had some potential as a storm sb card that is more versatile than just for the dredge matchup, it would be pretty easy to cast on turn one with rituals.
The main issue I see is that this is actually really bad as dredge hate, all they have to do is sandbag the bazaar activation to your EOT and go nuts on their turn.
Also worth mentioning that the ultimate is a win-con no matter what, it's hard to imagine scenarios where your opponent pulls out a win after you've had this guy active for a couple turns, then proceed to draw 7 cards.
I think Sylvan Library is an auto-include in this type of list since it helps you pull ahead on cards or find the combo faster and it synergizes nicely with DR shaman and the new Jace.
I would add Flusterstorms instead of the mana denial package to make the deck better at winning early and in the blue mirror. MD Island(s) is probably going to be a must in order to cast a spell with UUU in the casting cost.
This deck is basically Doomsday but without the constraints that make you soft to Sphere effects or having to play cards that do nothing on their own.
Wouldn't be surprised if this becomes a real thing.