This modular accessory for the Moto Z that reminds of the Motorola Photon Q is expected to hit Indiegogo soon and, if the campaign turns out to be successful, it should reach the market later this year.
http://www.notebookcheck.net/QWERTY-keyboard-slider-Moto-Mod-coming-to-Kickstarter.199258.0.html
While I want a keyboard slider phone and miss my old Xperia Pro, these addon accessories are unlikely to work well due to the weight distribution. Manufacturers instead need to make keyboard phones again.