HTC today confirmed that the HTC Sense 5 UI will be coming to select existing models as part of a software update. Timing is unknown, however the models are expecting the update include variants of the One X, One X+, One S, and HTC Butterfly. As is the case with other updates of this magnitude, some of the newer and more robust features may get scrapped due to hardware limitations.
HTC will be offering upgrades to some of its existing devices in the next few months, including global variants of HTC One X, One X+, One S and the HTC Butterfly. Also, note that some features enabled by the new HTC One hardware will not be available in the software updates.