I don't know why anyone would want that, but if my DS supported internet AND flash, my world would be complete. I mean, I could post here when my family is having a boring conversation, you could play a ton of games on flash, and much much more.
Just plain internet would still be worth the money. The touch screen makes the keyboard possible without the need for one plugged in, a small square in the corner of the screen makes for a mouse pad, A or B or whatever other buttons for clicking... yeah. You couldn't really type very fast unless you practiced on Pictochat, but... internet DS is going to be so awesome...