The Z1 will most definitely get 4K recording, either through an official Sony update or through the devs.
In fact, the Z1 will get almost every software feature the Z2 will have including tap2wake, 4k recording etc. The one I really want is the noise cancelling technology for earphones. That would be perfect.
Current Device: Sony Xperia Z1
Previous Devices: Galaxy S3 I9300, SE Xperia X10i