HTC 8X/8S 等机型暂无法升级到 WP8.1 Update 开发者预览版

Note: If your device is enabled for the update but no new version is made available to you: There are a small set of devices for which we aren’t offering the latest build of the Developer Preview program due to an identified problem that requires mobile operator or OEM driver updates. These will be offered when the official update for your phone is available.
以上是官方的解释，说是因为有一些问题，需要运营商或者 OEM 的驱动升级才能下载