Rumored specs for the handset include a display of 5 inches or larger plus a Snapdragon 800 or Snapdragon 805 processor running the show. The flagship device is also said to employ a twin-sensor rear Ultrapixel camera. These sensors should bring better focus, depth of field and overall image quality.
Other possibleof the device code-named "M8" are a 3GB RAM, fingerprint reader, and the familiar unibody metal housing. Presumably, the phone runs Android 4.4 KitKat and features the latest version of HTC Sense.
In terms of branding, HTC will reportedly stick with the HTC One name for this year's model. Much like Apple has done with the iPod and iPad, HTC may simply refresh the device with newer technologies.
As for when we'll finally see the new HTC One announced, Mobile World Congress seems to make the most sense to me. The massive trade show set in Barcelona and taking place in late February would give HTC a few weeks to prep for its new flagship arrival.