Did I get what from someone othe than uBeam? If you look at uBeam's pitch, with a fairly large array of transducers, they just have to get the cost per transducer under control or they can't get off the starting block. I have done quite a lot of work on ultrasonic utility flow metering, and currently its unclear whether water and gas meters will make a massive move to ultrasonic measurement, due to cost. The transducers are a key part of that cost. Various other proximity applications need cheap ultrasonic transducers to be economically viable, and are being inhibited right now. People like Murata, and various Chinese suppliers, really want to get costs to the point where more high volume markets can take off.
Indeed - there's a reason many of my blog posts discuss the cost of a transmitter or receiver. If it's a consumer device you need the COGS to be 1/3 or less of what you sell to the public at, so if you claim $30 for a phone case your COGS have to be $10. Assuming that's all in the transducers (not true, there's electronics etc), then for an iPhone X case at 14.4 by 7.1 cm it's approx 100 cm^2, or 10 cents per cm^2. Murata transducers which sell to car manufacturers in huge volumes are in bulk around $1 per cm^2, so that means you need a >10x improvement in cost on an area basis. You then also need to be transmitting at 145 to 155 dB according to uBeam, which is around 30 to 300 times as much power as the Murata devices (assuming a 130dB max at source for Murata). You also need to be smaller, so your element spacing doesn't cause grating lobes to be formed and insonify places you didn't intend, so let's say a factor of 5 in area per device. You also can't have a 1cm thick block on the back of your phone (thicker than the phone!) so they have to be much thinner, let's say 5x again, so 25x in volume total improvement. And each and every device has to work under all conditions, from arctic to desert temperatures, in a dry or humid room, with each and every one of millions of others made for years to come.
So 10x better on price, 30 to 300x better in power, 25 times better in volume, meet all other existing requirements.
As I said in my second blog post "In theory, it can be done in limited cases, but in practice cost and efficiency issues will likely render it impractical."