I Do plan to attend the conf. and since it will be work and NOT a family vacation, any flights over 7-8 hours would be an issue. So anywhere in US or Europe (and yes, I do love Prague, a lovely city.
I do love Cape Town (except having to drive on the "wrong" side of the road. Only demolished one wheel). and Australia and New Zealand are two of my fav. places, but with a Day + travel from the East coast, I would not be able to attend if at one of those.
I think the focus should be, where is the most "central" location, realizing that for SOME people it will be 24 hours away, but where in general terms would be the easiest to get to. Once you can generalize that location (i.e. USA, Western Europe, Eastern Europe, etc. ) then lets discuss where, in that location, people would like to have the event.
Just my 0.02 cents worth!