Doesn't Jonathan save Clark in the afterlife or something?
Wouldn't that have worked even better with him already being dead like the classic setup?
Martha still being alive could work, but I don't see the need for both of them. With Jonathan dead and Martha still around, it might give her the opportunity to actually be treated as a character and not just an extension of Jonathan. MOS was still more skewed towards Jonathan, but I appreciated Martha having more presence in the narrative than we typically saw at the time.
Because the middle aged couple were dead first and were dead for a longer period than when they were alive, whereas killing off Nora Allen just seems like a random decision for needless grim darkness. Whereas we have more than enough evidence of Superman not being gratuitously dark when the Kents are dead, like the first 50 years or so of his existence.