It was announced by HTC that due to Sense’s hardware requirements, only newest HTC devices (Flyer, EVO 3D, Sensation) will be able to support it.
From the examples given, it looks like your
current Desire, Desire HD, and even your new Incredible S or Desire S
won’t be getting the new Sense UI.
The EVO 3D and Sensation are both dual-core
phones, and the Flyer has a 1.5GHz processor so it is assumed you’ll
need a powerful phone for HTC Sense 3.0 to work.