Aside from reducing buffers and changing the queue management tactics, we're still interested in QoS and that's why we have tc filters, iptables MARKing, etc.

With regard to WLAN, what do you think about enabling or disabling WMM on WLAN NICs and ap/routers?

Supposing that applications or other mechanisms to proper DSCP or layer 2 tagging this should allow WMM to further do the prioritization on layer 1, however I've read a WMM-enabled station is like 4 stations competing for medium time. Is that analogy justified? Is that good or bad in terms of delays incurred by signal quality?