Well, I'm not completely sure but I would guess somewhere in the 2-3 month range. Should be around near the beginning of Summer Vacation. I think it should be possible based on the fact that the DSi uses banners which can be hacked like the Wii's program, bAnNeRbOmB. They are more encrypted than on past systems (the banners). Another way (I was reading this the other day on DSiBrew) would be to corrupt an image and to view it through the Internet Channel. The ups of this would be the fact that this is actually running in the DSi Native mode, meaning we would have access to the DSi's Camera's, Ability to connect to WPA encrypted access points and much more (playing sound, updates features). This could be a more realistic possibility, at least in the beginning. It has actually been proven that Opera can be crashed by a purposely corrupted image. You can find that on DSiBrew, or the Opera crash report database. The corrupted image would be a good exploit. I believe that Nintendo would have this fixed within a week, but we would know more information and be able to tell more about the DSi even if we only had a week. We could also just keep developing new images (most of the time, Nintendo is pretty dumb when they fix these type of things).
In any case, can't wait for someone who knows their codeing to get started on this. There are many at DSibrew, but nothing has been discovered yet. Another way you could help would be by downloading the DSi common key bruteforcer. If you happened to find the common key, upload it to DSibrew. Here is the link for the bruteforcer.

http://www.mediafire.com/?zjmtdybjlum