I don't think that she's Elektra. Of course Elektra is a given, but the background of her character doesn't sound like Elektra at all (She's the daughter of a rich greek ambassador who falled in love with a pre DD Matt, not someone that he met because she was trying to save Hell's Kitchen. Plus they were in college and not in Hell's Kitchen. Elektra never had anything to do with Hell's kitchen at all until she tracked down a criminal who was here and was, for the occasion, reunited with Matt), and I doubt that Marvel would change the Elektra character to fit Rosario Dawson, they are not Josh Trank.
But her being Echo, Milla Donovan, Kirsten McDuffie or Angela Del Toro (Never thought of that before seeing it here, but Rosario Dawson would be a perfect White Tiger) would work.
As for Melvin Potter, he's such a great and sympathetic (and tragic) character. I would love to see him on screen, both as a dangerous lunatic, and later as a reformed villain and now friend of Matt (I love his scenes in Born Again)