If I wait long enough (~10 min) I can see deep sleep as used, but with 0:00:00). I have tested the kernel from FXP 109 with Oodies MIUI V4 alpha 1, and there I get deep sleep again, so in the kernel itself deep sleep is enabled again, but there's anything in the rom left the prevents the device for me to enter deep sleep.
Also kgsl isn't crashing on MIUI V4 aplpha 1, like it did on earlier cm9 versions when the device entered deep sleep.
[HOW-TO]UNLOCK bootloader for SE XPERIA X10
Recovery: CWM 22.214.171.124 touch
Device: Google Nexus 7
Recovery: CWM 126.96.36.199 touch