As good of an idea as it is, I don't think it will happen. If you know when Target has what you want, you won't go as often. When you don't go as often, then you aren't as tempted to pick up that new movie that you wanted to see, or try those new potato chips. For me, when I go on a toy run and start coming up empty handed, I'm lured into buying other stuff that I may or may not want.
For example, I went to Target last week. No toys to buy, so I picked up the new Coldplay album. If I knew when Target had the toys I wanted, I would only go to Target to buy toys. All of my music purchases would be reserved for iTunes, food purchases would be reserved for Food Lion or Lowes, etc. That would cost Target some business, so that's bad for them.