Preliminary benchmarks of new network APIs like netmap are showing 20mpps between guest and host for untrusted guests and 70mpps to trusted guests, and scales near linearly with more cores. With that many pps per guest, why not let the host do an AQM? High end service NICs support multiple virtual devices where you can tell the NIC to evenly distribute bandwidth among the virtual devices. It's already mostly a solved problem, just some people reinventing the wheel. I know FreeBSD is currently looking at adding netmap to connect the guest to the host so the guests can do line-rate 10Gb and almost 40Gb.