@upleaks - a pretty reliable source until now - reiterates what it was first mentioned in October: HTC will use a different naming scheme for the successor to the One (M8). Right now, the smartphone is codenamed HTC Hima, and is expected to be released in March 2015. Reportedly, all major US carriers will offer the Hima, which is already being tested in carrier labs.
Last we heard, the upcoming HTC flagship was supposed to sport a 5.5-inch display with 1440 x 2560 pixels, and a Snapdragon 805 processor. However, according to @upleaks, the display is a 5-inch 1080p one, while the processor will be a 64-bit Snapdragon 810 (with four cores clocked at 2.0 GHz, and four cores clocked at 1.5 GHz). Other features may include VoLTE, 3 GB of RAM, a 20.7 MP rear camera, and a 2840 mAh battery. Interestingly, the front-facing camera could be either a 13 MP one, or a 4 MP UltraPixel one. The new handset is expected to run Android 5.0 Lollipop with Sense 7.0 UI.
It’s said that there will also be an HTC Hima Ace - a more affordable version of the flagship made for China (and featuring dual SIM support).
We can’t confirm any of the details above, so for now nothing is certain - other than the fact that HTC is undoubtedly preparing a new flagship Android handset for next year.