We have an official statement from HTC's Jeff Gordon:

"We are excited about the latest update for Android, Ice Cream Sandwich, and are currently reviewing its features and functionality to determine our upgrade plans. Our goal for Android updates is to give every customer an improved user experience, which means balancing each phone's unique hardware, HTC Sense experience and the Android kernel. While our goal is to upgrade as many of our recent devices as possible, we are committed to maintaining every phone's performance and usability first. Please stay tuned for more updates on specific device upgrade plans."

In other words, anyone who recently purchased an Android HTC device has a good chance of seeing ICS come there way in the future, but there's no guarantee.