...Also I should add that the above is very much talking about the long-term ideal architecture. Right now IIUC everyone's still focusing on figuring out how to make buffers smaller without killing throughput. I think this is basically the wrong question -- we're going to want big buffers anyway -- but no-one's even thinking about power consumption yet AFAICT.
And in the long run, packets will be dropped intelligently according to some control law that tries to maintain fairness and provide useful feedback to senders (i.e., AQM). For now we mostly use the "drop packets when the buffer overflows" rule, which is a terrible control law, but may be less terrible with small buffers than large ones.
So in the long run buffer size doesn't matter, but in the short run it's a single knob that's coupled to a ton of theoretically unrelated issues, and decoupling it is going to be a pain.