Asus has scheduled a Zenfone 5 announcement for February 27 in Barcelona, and the way the company usually does things makes us think it won't be just one Zenfone 5. If anything, the #backto5 tagline could be closer to the number of devices we may see at MWC, in addition to being a shout out to the already existing Zenfone 5s. Just Asus things. Anyway, one of these Zenfone 5s has been revealed in a manufacturer's manual sporting an (aluminum?) unibody and a tall 18:9 display, likely in the 5.7" ballpark. Carrying an internal designation X00PD, it's unclear which model exactly this...
Source: https://www.gsmarena.com/asus_zenfone_5_renders_surface_out_of_a_manual-news-29459.php