I hope not, just got a DS.
I remember back when I got a Gameboy (still black and white). It was a black case, which just came not long before I bought it. About a month later Game Boy Color came out. I was kicking myself for not waiting.
I think handhelds should be replaced about the same speed as consoles. Give the device 2-3 years of attention before bringing out a new and improved handheld, otherwise people will be upset with themselves for not waiting on the new and improved version. Also could further alienate some owners for the recently outdated handheld if new games only work on the new improved one.
I've heard rumors on here but that's about it. Nothing from solid sources.