@upleaks has it that the Lollipop update for the One (M8) will, in fact, be released with the current version of Sense UI (Sense 6) - because HTC has yet to start porting Sense 7 to the handset. Of course, for now we can’t be sure that this is how things will go - and we won’t be sure until HTC actually launches the update.
As previously announced, HTC is committed to bringing Android 5.0 Lollipop to the One (M8) and One (M7) within 90 days of receiving the final software from Google. Thus, the update should be available to end users in January 2015 the latest.
HTC did not confirm the existence of Sense 7 UI, but it seems that this has a Material Design-inspired look. You can see the alleged Sense 7 UI screenshots that we mentioned earlier in the slideshow below.