In short, my vote is "delay until it works with all OS and 7.8".
Agreed. An important idea behind the original scheduling of the HP releases is that the dust should settle from the the latest GHC release before shipping an HP that uses it.
The HP is about stability and reliability, not latest and greatest. That means I don't use the HP, but that's okay with me because I've already agreed to pay the early adopter's tax.