According to @evleaks, the M8 will be the first HTC smartphone to have on-screen buttons. This means that the space used by the hardware buttons (and the HTC logo) on the original One will be taken by the extra screen estate. So the M8 might have about the same the size as HTC’s older flagship, while sporting a larger display.
One of the advantages that the use of a 1080p display instead of a Quad HD panel could have is a (theoretical) longer battery life. As a recent poll of ours is showing, a long-lasting battery is among the most desirable features that customers want in a smartphone. So maybe HTC will use this as a main weapon against the competition.
We One 2, or One+, or something else. Let's hope that official details will be unveiled soon.