HTC will most likely follow up the One M9 with the M10 flagship in 2016. Fans expect that the M10 will be a large improvement over the somehow disappointing predecessor.
HTC One M10 Specs
5.0-inch 1080p / 2K Screen - the previous One M series phones had 1080p screens. It may be time for an upgrade on the screen resolution. HTC might also add a bit more in the size, but they could still stick to the same formula for their previous phones. A 1080p phone could also last longer as there would be less screen space and pixels to render.
Snapdragon 820 and 4GB RAM - if HTC does decide to upgrade, they could go in the direction of more RAM. The M9 has 3GB and is more than enough for multitasking, but more RAM would not hurt. There is also hearsay that Qualcomm's Snapdragon 820 could power the device.
Waterproof Feature - the M10 could possibly be waterproof to an extent. However, there have been little to no details about the feature. It could be waterproof for splashes but not really submersible for long periods of time or deeper waters.
Android 6.0 Marshmallow - almost all 2016 smartphones would most likely run the new Android version from Google. HTC has also confirmed that the M9 phones would receive the update soon, which adds weight to the possibility of the M10 running Android 6.0 out of the box.
Fingerprint Scanner - the scanner will work in tandem with the Android 6.0 Marshmallow for better security features.