I'd agree that we shouldn't see Bruce, simply because there is no power to him as a character when he's still only Bruce and has years before he creates the Batman persona. GA is a good substitute for him in this regard and its to the writers credit they have used Oliver instead of taking the easy route with Bruce. (That said - Bruce and Clark did meet as kids in a Weisenger era story.)
And anyhow there are plenty of other JLA members that can show up. The writers seem to be forging their own direction anyway and adapting the bits of the history they want, and even keeping some great Silver Age flavour instead of going the "dark brooding" route.
Vaguely familiar names show up but they're giving them fresh spins. Such as Bart Allen instead of Barry. Arthur showing up was excellent. (Wonder how many others of the JLA Lois has snogged before she settled on Supes?)
There'd be little point to Hal showing up, sans ring. But then again Hals strength is his strength of will and character, so perhaps it would work. Diana maybe. Can't imagine Carter as any of the Hawkman incarnations. Ray doesn't invent his abilities till later, though again this can be changed I suppose. Jon - hmm - a martian in Kansas might make for some good racism analogies.
I'm curious about the eventual fate of Chloe, since given she is the one character not from anywhere in the legend anything can happen to her.
Oh - and I choose to think Harvey was still black in #3 - just the acid bleeched his skin (Michael Jackson anyone?).
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6000 years ago, God made the Earth exactly as it is now: flat and in the center of the solar system.