私が更新内容を最後まで見ていなかったので見落としていた内容を明記しておきます。
以下が原文です。
取り扱い可能なPSDファイルの要件。
また、OIIOのインプリメントに基づく使用制限です。

What works:
===========
* 8bit images (with or without alpha)
* 16bits images (alpha discarded)
* Photoshop files saved with 'Maximum Compatibility'
* Cycles, Blender internal, BGE (and player)

Known limitations
(due to OIIO dependency):
=========================
* Images with less than 4 channels show a wrong thumbnail (bug may be in OIIO)
* Packed images are not supported
* We do not write PSD files.

Note: old Blenders have support for PSD via Quicktime library. But due
to license issues this was discontinued.