This should be HTC's game plan. Have 2 models.
M9: Improved 4.7" 1080p display, 64bit processor, 3GB of ram, 32GB of storage,a regular 16MP camera with optical image stabilization and high MP front shooter, get rid of that silly black bar below the display, loud boom sound speakers, removable battery, sd card slot and strong IR blaster. Make it the same size as the iPhone 6 and you have a winner.
M9 Max: All of the above spec's but with a 6" 2K display and larger battery.
Pretty simple in my book. There is no need to but a 2K display in a sub 5" device. The overall screen quality on my Note 4 vs Note 3 is much better but I can't tell the difference resolution wise between a 5.7" 1080p vs a 5.7" 1440p. And don't attempt to release a fingerprint scanner. Lollipop has a trusted device option with Bluetooth and NFC pairing. With smart watches getting cheaper and NFC rings unlocking your device it will be easy.