Currently you can set speed limits to a group, but what it does is set the same limits to all torrents in a group.

What I'd like is that the limit is set to the group, so if I say "limit upload to 100kb/s" and also a group priority system, counting all active torrents in such group would never pass such limit. This way, we can be sure that low priority groups can fill the bandwidth when it's free, and reduce its usage to a limit when other higher priority torrents (by group) get active so they get as much bandwidth as possible.

*edit*

So in "group policy" you could add a "maximum transfer rate for the entire group", in kb/s, and "group priority for available bandwidth", which could be a number between 1 to infinite, or for example, a percentage. So if I give a group a percentage of 100%, that group will have all the available bandwidth even when others are active. What if we have groups with 100%, 80% and 30%? The 100% gets all it wants. From the second one, it gets up to 80% or more if it's available. For the third one, it gets 30% or more if it's available.

I find this idea much more practical than the queue system and setting speed limits torrent by torrent. But due to the fact that some torrents can be in many groups, I don't know how to implement it exactly. Maybe just apply the best group policy applicable to a torrent? Other than that, I think this idea doesn't need too much for implementation since there's already a good transfer limit system to work over it.