According to Nikkei Trendy, 3DS Lite is coming - thickness and runtime improved (longer battery life).
http://jin115.com/archives/51838525.html
Personally I don't care. If anything then the 3DS is too thin - I have already bought a $10 grip and am very happy with it. As to battery life, while longer battery life is always better, I manage well enough with what I have and certainly wouldn't go through the hassle of trading in my current 3DS just for that. Also, it doesn't seem as if there is a date set to this yet.
Now if it were a 3DS XL...
[edit] Apparently it's not even a rumour but just speculation... ""Will 3DS Lite Make an Appearance? To continue the spread/momentum, a version addressing the 'weak points' (thickness, runtime) is a possibility."[/edit]
Currently Playing: Shin Megami Tensei: Devil Survivor Overclocked, Professor Layton and the Curious Village
Anticipating: Xenoblade, The Last Story, Mario Kart 7, Rayman Origins, Zelda SS, Crush3D, Tales of the Abyss 3DS, MGS:Snake Eater 3DS, RE:Revelations, Time Travellers, Professor Layton vs. Ace Attorney, Luigi's Mansion 2, MH TriG, DQ Monsters, Heroes of Ruin