A feature that I miss dearly from other bittorrent clients is the automatic prioritization of completed torrents according to seed/peer ratio; sometimes with a minimum seed threshold. I've checked the latest version (beta and SVN changelog, though that's incomplete with the SVN changes), and have done some searches for potential plugins to no avail.

I'm not well-versed in C++, so it's unlikely I could produce anything in short order; however, I've a good idea of how the process itself would go, and I suppose that's a start:
- Request and receive announce from trackers for completed torrents; is some resolution required for update intervals between active and queued torrents?
- Perform ratio comparisons and determine order; obey max seed ratio.
- Alter active torrents and queue order.

I agree.

I never use Download/Upload ratio because it is relatively unimportant.
The Seed/Peer ratio is much more important. I always manually announced all my torrents and manually seed the ones with the least Seed/Peer ratio.

Is it really just that nobody thought of it?

I know some C++ and have free time if somebody is willing to show me the hoops.(Never developed for oss before)