I was running XPR V7 R1.5.18409 on my HiPath 4000 V5 (RMX V5 R1.6.38 / UW7 V5 R1.2.8). We use SIP connections. I'm not sure what "new features" aren't supported, but as a basic voicemail platform it works great.
LoPath
Maintain HiPath 4000 V5 & V6, OpenScape Xpert V4, OpenScape Xpressions, OpenScape Contact Center V8, OpenScape Voice V9