I very much like the idea of automatically requerying the network for a file in the case where you try to resume a download on startup -- this is the ideal place for this kind of feature.

The delicate part here is that automatically sending searches out on the network has the potential to create a LOT of traffic -- it could potentially double the messaging traffic on the network if not done carefully. This is why we have not yet added something like this.

There's definitely room for a nice feature addition in this general area, we just have to work out exactly how it would work so that it doesn't do more harm than good. Other clients have done this (Phex, I believe still does this), but they are only really able to get away with it because they just aren't that popular, so the effect, while surprisingly detrimental in our studies, does not grind everything to a halt.