In case any of you were curious what the "Abyssal Genasi" article is, it's basically Quasi-Elemental Genasi. I'd say at first glance they do in fact resemble some of the ideas that some of you have came up with for 4e Genasi of other manifestations.
The main fluff is stuff about how they are corrupted caused by the corruption of the Abyss, but that can easily be re-fluffed to the Negative Energy Plane. The 'corrupt manifestations' are Causticsoul (acidic, water-breathing and can turn into a wave of acid), Cindersoul (ash genasi resistant to fire who can suck the energy from an attack), Plaguesoul (a poisonous type of genasi) and Voidsoul (Vacuum Genasi that resist psychic and can blink out of existence). I could easily see salt, dust, and ooze among some of the less obvious choices for those manifestations.
Normal genasi can quite clearly take an extra corrupt manifestation, and these genasi can do the opposite. Paragon Paths are some Demon-fighting one which isn't too interesting, followed by the much more interesting water-acid Soul Of Erosion, and really interesting Scion of Absence which can do things after looking to the void and would probably fit right in with either the Doomguard or the Ciphers.