At some point, I'm convinced the "conference structure" is going to fall apart.
Case in point -- I haven't bought my tickets yet for SIGCOMM because, unless I'm missing something, a schedule isn't up yet, and unfortunately, because ACM has scheduled a SIG chair meeting overlapping with SIGCOMM (which I don't understand also, but perhaps beside the point), I want to see what's going on when at the conference to plan my timing.
6+ weeks out, round trip tickets from Boston to London are over $2500 on nonstop economy flights. And those don't seem to be on US carriers; since I have to stop back through New York for this other meeting, and I need to find a US carrier (or figure out if this is a case where it's an exception to what is the currently believed NSF policy), tickets look to be well over $3000. Then there's registration, hotel, etc.
At some point, this becomes unsustainable, I think.