While many of Jon's Justice League members are young heroes, Yara Flor's refusal is an interesting one since you'd think she'd want to join in. But, well, the events of Trial of the Amazons showed her that the Amazons were real cruddy and Diana practically plopped the title of "Wonder Girl" onto her to save face. So, she wouldn't want to do anything like teaming up after all that.
At first it seems odd that Superman's ideal world in his Worlds Without a Justice League story is one where Darkseid has taken over most of the universe, and he's basically trained himself not to think about it. It doesn't have much to do with the main point (getting to see Jon grow up), and it's pretty uncharacteristic for him to be okay with it. But he's been pulled specifically from The Warworld Saga, where he's left Earth to save people from Mongul and doesn't know if he'll ever see Jon again. Right now, his perfect world where he's there for his son is one where he's not the kind of Superman who'd have made that decision.
