At least until the actual books come out and I have a chance to read them. And it is this-- I really don't think they need to start with origin stories. Unless at some point an origin flashback is necessary for the plot to proceed and the story themes to develop, there's no real reason to rehash how Superman and Batman came to be. One thing that made All-Star Superman work so well-- besides the outstanding quality of the writing and art-- was that it gave us an iconic, fully-developed Superman.
Sure, Grant Morrison did a lot of nostalgia referencing in All-Star Superman, but note the verb tense. Did. It's been done and done well. Ditto for numerous retellings of Superman and Batman's beginnings. All-Star Superman took elements necessary to the stories but freed the Superman concept from the creativity-crushing effects of having to shoehorn monthly plots into this overarcing universe narrative. Instead, we readers got a basic, cleaned-up Superman who seemed fresh yet comfortably familiar.
I know there are more fans who feel if the story's not part of the ongoing DC narrative-- if it's not "canon"-- then it somehow doesn't count than fans like me who simply want a good story taking the best elements of the characters. To canon fans, quality is sometimes secondary. They want to feel as if the story they're reading is part of the character's official biography. Otherwise they feel cheated.
Actually, the characters don't need to be "rebooted" or "revamped." They're fine as they are. They just need all the years of crap surgically removed and allowed to stand on their own again. And hopefully these Earth One books will do that for Superman and Batman and let us see exactly what it is we so enjoy about the two of them in the first place.
But I honestly don't want to read one hundred pages of something that seems like a half-assed Smallville adaptation or a paler version of Batman Begins.