How long will Nintendo keep the DS going?

I'd say, this decision would be up to the developers. Now if you're referring to first party software, I wouldn't expect much support if any.

With a few good titles still to come like Pokemon Black/White 2 the DS still has some life to it, and even after that it'll be selling for quite a while. Nintendo just need to release those anticipated 3DS games so that new buyers actually desire a 3DS over a DS - because right now buying a DS is still a very good idea if you dont have one.

Besides DSiWare the DS seems pretty much done.

sorry to say but i have to agree. DS honestly is overused DSi i think honestly they shouldnt have too many more. and Wiiware well whats the point of putting them on their when Wii U E shop has 50x more room. My opinion But its kinda true though.

Yep as of later in June DSi won't matter (with Flipnote 3D) plus this is good it made the best selling console, now it's time for 3DS to overthrow DS