Not long ago when the first Raspberry Pi came out I was surprised to learn so much computing power crammed into such a small footprint and for just $35. Then the RPi 2 came out, for the same price. Not long after that the RPi 3 is already out and the price is the same! Wow. And the CPU is 64-bit.
If the RPi can run either Windows (not the IoT version) or OS X it could definitely go mainstream. There are companies that put an RPi into a nice box with monitor, keyboard, and mouse but these are too expensive when compared to 1-2 year old full-blown notebooks that are only $200-$300. I'd love to see a fully packaged RPi running Windows or OS X for $150.