Right, I don't think the ZD can do this natively, and it probably isn't trivial to implement either since the ZD is an independent observer to the traffic flow at each AP. It's easy for each AP to implement a per-client rate limit, but limiting the overall per-WLAN/per-VLAN traffic would require a lot of AP to AP coordination.
This seems like it should be done either by a firewall/UTM with prioritization / rate limiting features, or a dedicated traffic equalizing appliance.
