Anybody who wants to unrestrict Flash, I will offer to play you for $10/game at Eternal Weekend this year if I get to play 4 copies of Flash vs. your current deck. You will regret it. The deck should not be using the kill conditions mentioned above. It should be based on the article I wrote last year, with Show and Tell. You do not rely on the graveyard, but utilize it better than anyone else. Serenity + Hurkyl's Recall makes the Workshop matchup a joke.
Having access to both Omniscience and Bargain totally changes the calculus as compared to previous iterations of Flash. Giving the best color an even faster (effective) game ending 2 mana spell at instant speed is a very, very poor idea. I'm not sure how unrestricting Flash does anything to change the power and effectiveness of unrestricted Mentor decks (and the corresponding metagame), which have 4 copies of arguably the best kill condition ever printed.
What is nice about the deck, as you say, is that it doesn't rely on the graveyard, because you can just use Show and Tell. But it certainly wants to be able to use it's graveyard. Rector can't trigger with Leyline in play, nor can you flashback Therapy. Gifts/Will is pretty awkward as wlel.
This deck is definitely more difficult to hate out then the Flash decks I was brewing above, but it's also definitely alot less consistent in terms of being able to assemble the Flash combo. With Leyline in play, all you have to do is counter Show and Tell and your deck is largely dead in the water.
It's probably just as viable to do what Dredge often does, and bounce the hate rather than try to play around it like you do.
I'm not saying this isn't a good deck, I just don't think it would be dominant. Vintage has so many tools for combating these types of decks these days.
I said you would start with the deck shell in the aforementioned article, not use it as printed. You would want to dramatically lower the mana curve, and will not play 4 Gifts (1-2 will suffice at that point when you have 4 copies of Flash), because Gifts is more of a game-ender in that scenario. The consistency and power with 4 Flash and 3-4 Show and Tell is much more powerful than any combo deck we're currently seeing in Vintage at the moment. That is not a good thing, contrary to the claim that the format can/should be sped up by a turn (which I think is a poor idea also).
I'm not sure how unrestricting Flash does anything to change the power and effectiveness of unrestricted Mentor decks (and the corresponding metagame),
The idea of unrestricting Flash is an alternative way to deal with a metagame that is strangled by Shops/Mentor. It doesn't do anything about Mentor directly, except create a deck that could compete with it. Unrestricting Flash either creates new decks or strengthens an existing, marginal strategy. I don't think anyone can dispute that from a purely logical perspective. The issue isn't whether unrestricting Flash would do that, the question is whether the costs of having that kind of deck outweigh the benefits.
I understand this sentiment, and don't think giving the format a more busted combo deck is a great solution. People are doing well enough with Outcome and Gifts decks, and frankly are still in the beginning stages of innovating and adjusting those to compete with Mentor and 9Sphere.dec Workshop variants. The point of my comment is that Mentor is likely the best kill condition in Vintage, by a long shot, and simply adding an unfun and busted combo deck to the format isn't going to do anything to cure the ills of Vintage, and bring back people in to the fold who are sick of it at the moment. The card Mentor itself has done far more to push out other decks and strategies than any perceived damage that Gush or Gitaxian Probe ever did.