Why to wait on 4K

I've seen a few people start getting excited about 4K TVs, monitors, and more, and I keep coming back to the same question: Why is everyone buying them now?  Don't get me wrong, higher resolution screens are nice, and 4K screens look fantastic, but that's not the next step in resolution jumps.  In fact, 4K is just a beginning step, and upgrading this early on is kind of like buying a 720p television when HD was just coming out: It's better to wait!