I hate cutting people off if they might only be a few minutes (or even seconds) from completing their download.

Would it be possible to show how much time remains before a remote user's download is completed?

I think it is possible but it would be very inaccurate. You can see other peer's completed percentage and download speed so theoretically you can calculate ETA, however the download speed often fluctuates wildly so ETA based on that will be useless, changing constantly. Moreover the download speed of other peer's is an estimation already.