Unfortunately, DC doesn't accept unsolicited writing submissions. But if they did, what's the one story (or group of stories) you'd place your best shot on? It would no doubt have to be about a character or set of characters you know extremely well, and give an angle creative and different enough that it stands out. I'm not really asking what you think you could create that DC needs in the current climate per se, but rather what story you think would grip a reader enough for them to give you a call back.
Writing a comic book story arc is something I'd like to accomplish just for fun out of my love for the characters. I don't think I'd get published, but it's fun to think about and I'd like to think what I come up with is something that other fans/readers could relate to and appreciate. My most recent idea is a Justice League story where the antagonist(s), whoever they end up being, try to destroy the league not by external attack but by internal implosion, preying on and manipulating the existing personality clashes and vulnerabilities of each character so that it caves in on itself. Not necessarily driving them to hate each other, but making their personal priorities shift and cause conflict with their commitments and each others' priorities.