While Sony's Xperia Z4 is still waiting to be officially announced, the rumors and speculation surrounding its specs and release date are already rampant, pointing to Q2 2015 for the timeline that we can expect to see the new device. 

The Xperia Z4 was expected to be announced at Las Vegas' CES 2015 earlier this month, but since that didn't happen, many are expecting the next logical time to be at March's Mobile World Congress in Barcelona, Spain.

The latest rumors point to the Z4 keeping the Z3's metal frame but adding in some new colors for the design. A waterproof micro USB port is also on the rumor list, something that Sony is including after some problems with that same port on the Z3. Getting that IP68 water- and dust-proof certification is important for any new smartphone these days.

The rest of the rumored spec list includes a 5.2-inch screen running at 2560 x 1440 pixel resolution, a 1.5 GHz Qualcomm quad-core Snapdragon 810 processor, 4 GB of RAM, and 32 or 64 GB of storage, upgradable to 128 GB through micro SD.

An impressive 20.7-megapixel camera is said to adorn the rear spot while a still-impressive 5-megapixel camera will be up front for high-quality selfies.

But perhaps one of the most interesting rumors about the Z4 is the talk of the new Sony Walkman edition of the smartphone. According to a new leaked image spotted by iGeek, the Walkman version would concentrate on being a music player by offering hi-res audio codec support, a two-day battery life, and S-Force PRO front-facing speakers. The Walkman edition is also expected to come in a variety of flamboyant colors, which may be in connection with the previous color design rumors floating around before this one.

This Walkman edition could be in response to the popularity that Apple enjoyed with the iPod (enough to make it a separate device from the iPhone still), but it most likely is in response to the popularity that the Walkman name has seen resurrected after the Guardians of the Galaxy movie launched late last year with a classic audio tape Walkman front and center.

But the Xperia Z3 is still going strong as Sony's current flagship phone has been confirmed to get the Android 5.0 Lollipop OS update in February along with the slightly older Z2.

A manual download is available for the Z2 and Z3 now on the XDA developers forum, but that software is experimental and doesn't include all features that are found in Lollipop. The question is, though, will the two phones update to 5.0 or straight to the latest 5.0.2.

The Z2 and Z3 are not the only existing Sony devices that will be receiving the Android Lollipop update, though. Sony has confirmed that the mobile operating system update will be coming in "early 2015" to the Xperia Z, Xperia ZL, Xperia ZR, Xperia Z1, Xperia Z1S, Xperia Z Ultra, Xperia Z1 Compact, Xperia Z3V, and the Xperia Z3 Compact.