This card would break the game. The reason is that it would require players to remember everything that happened in a turn. Now, most turns are simple, you may play a couple spells and attack with a few creatures. However, what if you draw 15 cards, flicker 3 creatures, extort 7 times. Yes, you could maybe work out something really close to where you were at the beginning of the turn, but you cannot always be 100% right. This card's existence would require players to record every action they make during the every game and secretly record what cards they draw each turn. That is really the killing blow to the card, players easily being able to cheat which cards they drew in a turn (way worse than Sylvan Library).That rant aside, if you still wanted to print this card, I would reword it for clarity like this: "If it is your turn and no library has been shuffled, start the turn over. (The game state is set back to the state it was in at the beginning of the turn.)"
That still creates groundhogs day situtations where you can just cast this over and over. And whose to say which card you just drew? I think your best bet would be:Redo 3UUSorceryTake another turn after this one. End the turn. You may only play this card before combat.
Actually, even better:Redo 5WUSorceryEach player returns to the battlefield all permanents in his or her graveyard that were put there from the battlefield this turn and gains life equal to the life they lost this turn. Take another turn after this one.Exile Redo.