The 8086 was designed to be a 16-bit 8080, and 16 times the address space of that chip was a nice incremental leap forward. If you didn't expect the chip to become the foundation of the PC industry for the next 4 decades, it was probably a reasonable choice. At the same time, Intel made the iAPX432 chip, which was the one that was supposed to be future proof and look how that turned out.
