IBM has released HMC 8.8.4 as of 9/14/2015 IBM has not provided support for this version of HMC with IBM PowerVC 1.2.3 (or any prior release). If you are using IBM PowerVC do not upgrade your HMC to this latest release yet.
IBM support statement will be documented here if changed.
currently only 8.8.2 and 8.8.3 are supported
Have fun and keep waiting.. like us 🙂