Foldables are not the future of the smartphone, but its an important niche, just like every category Apple got into with the iPad and iPhone. The company realized some people just want big phones hence the iPhone 6. I also think its a similar case for the iPhone Mini. I think relative to the industry, the Mini is likely a success, but based on Apples standards, they don't see it that way. But, I am not surprised if Apple externally is testing this, its just logical for them to do so. Exacting standards which is the display technology is just not where they want it to be.
If corporations figure out a way to pull it off, it is likely it will become the present of cell phones.