Yeah I think it would be great for shoes or sports wear like they show in the video and for tents it would be great. I remember this one time I was camping and it a huge rain storm came out of nowhere, in the morning I woke up and everything inside the tent was soaked and needed ringing out. Its not actually the top that needs the water proofing from my experience but the bottom. The top already does a pretty decent job at keeping out water because of the angled roof, but the ground is being pushed into the wetness by the weight of whatever is in the tent and always soaks through eventually.
As for phones, I wouldn't do it myself but it would be great if this feature became standard in all phones like the Galaxy S4 Active which is water proof. Doing it yourself would probably either be messy and end up ruining the feel, texture or the buttons on the phone or involve opening it up with a screwdriver and coating all the electronic components.