Sense 7 UI hasn’t been officially announced, but said screenshots may indicate that HTC will launch this new version of its UI at the same time with upgrading its flagship smartphone to Lollipop.
@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.
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.