The bigger point here is NOT how fast the big DD motors (1000w+) will allow us to go. They're going to use a tremendous amount of battery power to do that other than in short bursts, making those kind of speeds impractical. The bigger point, to my way of thinking anyway, is their ability to provide large(r) amounts of starting torque - approaching that of popularly used gear drives - without requiring/using huge amounts of power, and without the down sides related to gears. They can also be limited as far as how fast they can go. That's what's going to make them popular.
I'm assuming that most people are never going to commute more than say 40-50 miles a day on an ebike and it sure seems like with the next generation of batteries (the 21700 Tesla cells and projected solid state batteries a couple years out) will provide enough capacity to provide that range. I'm assuming that most riders are going to participate in the power delivery until the cadence is just too much. The higher speeds can still be supported via a very high cadence but the rider really will not be providing any significant power, but I believe a total capacity of 1wh-h to 2kw-h is addequate to provide this range on an ebike capable of assisted speed as high as 35mph. I don't believe this will be exotic tech .... it's not even that exotic now - a 52V / 40A direct drive hub motor drive system is not that extreme and some smaller geared hub motors can run at lower power and provide the necessary torque but I would argue they would not be as reliable long term as the gears are certain to need replacing occassionally (not a big deal if designed for simple replacements).