A new Sony mid-range phone is in the works, its existence given away by GFX Bench. The Sony E2003/E2033 looks like a successor to the Xperia E3 with a 4.6" qHD screen (540 x 960px) and a 64-bit MediaTek chipset.
The chipset is MT6752 with four Cortex-A53 cores (at 1.5GHz), coupled with 1GB of RAM and a Mali-T760 GPU. There's also around 5GB of user-available storage pointing to 8GB total. The phone runs Android 4.4.4 KitKat, surely with Sony's usual skin.
The Sony E2003/E2033 has s 5MP main camera that shoots 1080p video and a 2MP front-facing camera that goes up to the unusual video resolution of 1,600 x 1,200px. This is a single-SIM device (at least these two versions are) and the chipset supports LTE though that's not something that the benchmark can detect.
Sony has a MWC event for March 2 and while we are not sure if it will feature the Xperia Z4, this E2003/E2033 mid-ranger might show up to fill in the ranks.
The whole thing sounds almost exactly like the Xperia E4, though that one has a bigger screen (5") and a 32-bit processor (based on Cortex-A7). That one has a model number of E2105 and was previewed in December, months before it's official unveiling.