I dont know what enabling QoS means on routers: is it traffic shaping or using QoS code points. Traffic shapping should be possible but I am not a strong believer of middleboxes tampering doing this (they probably dont have enough context to do it right). I'd rather have the applications or the browser or the kernel of the endpoint do this. For the latter this is kinda impossible because the QoS are ISP-specific and the application or middlebox should be aware of the them. Since there is no global solution or generic DSCP codepoints using them is not possible, however, there are some proposals in works to make generic marking possible.

The routers can enable WRED to mitigate some congestion problems, though it is not the silver bullet and works on a per-flow basis. Some new solutions to solve the buffer bloat problems is to install the experimental CeroWRT firmware in your routers (http://www.bufferbloat.net/projects/cerowrt), however, this is also a work in progress.