HTC earlier announced that Android Lollipop for One M8 and One M7 will be ready in 90days from launch, while competitors are already rolling out update as Samsung Galaxy S5 is already on Lollipop, so is the LG G3. This has resulted in faster work on HTC part to get update ready before CES 2014, scheduled for 3rd January 2015.
Android Lollipop 5.0 consist several new enhancements and as Sense UI is deeply customized HTC needs to port proprietary apps thoroughly before seeding an update, hence its taking longer. The next update will feature all features of Sense 6 UI and add to the sweetness of Lollipop like all new material user interface, ART runtime, encryption, new notification panel and much more.
So be ready to get Android Lollipop for HTC devices soon and the devices to be updated first include HTC One M8 and M7 and slowly thereafter rest of lineup will be gradually update to Android lineup. As of now HTC Desire 820, 816, Desire Eye and HTC One E8 are the confirmed candidates.