Finally this is becoming reality: Hardware Keyboard for MOTOROLA Moto Z, via Moto Mods. So far things are looking very promising but I have two things in my mind:

1. Size
Moto Z is pretty massive phone (153.3mm long) so it can be hard to reach the buttons in the middle of the keyboard. I did a DIY qwerty slider Android phone with Xiaomi Mi4C (138.1mm) and iPhone 6 (138.1mm) keyboard case. For my hands the length was absolutely maximum. Anything longer would have been too much. Now I'm using my Droid 4 daily and the length (127mm) is comfortable.

Because of that I'm suggesting to split the keyboard. Something like these: LG Protype, Dell prototype. In the middle there could be touchscreen, touchpad, speaker or extra buttons (for camera maybe?). It can also just be empty for lowering costs.

2. Software
Moto Z is a Android phone. It is possible to port Sailfish OS to Moto Z for example but it is not easy job. Like r0kk3rz already pointed out that Moto Z family is lacking CM13 ports. (Even Droid 4 doesn't have Sailfish OS port even though it has good CM support). Another thing to worry about is how the Moto Mod will work if we ditch Android? OS development will need special support.

Anyway I hope this will become reality. Keep up the good work!