It doesn't have to be too fancy or complicated; all it needs is an option to set a system-wide bandwidth limit (like 20Kb/s for example) and it would be nice to have a way to toggle it on/off (preferably by widget or ongoing notification).
If nothing like this exists currently and somebody manages to make an app to fill to void, I'd say a donation is definitely in order.
So, does anybody know of an app that would do this? Or would someone be willing/able to write one...? I don't know nearly enough about Java to do it myself.