L7 inspection is possible with firewall rules, but manual classification depends on the (class) structure of the shaper.
Generally it seems favorable to depriorize “harmfull” traffic at its source (set dscp/prio in torrent-client) and then have a qos-system that respects that marking.
The Topic of per-host fairness is hard (think ipv6) but beeing worked on in cake devel.
On the other hand: having a working simple.qos out of the box or better a recent cake should mostly alleviate the need for users to mess with this stuff at all.
I think we should stick on getting the basics 