Ok, seen this discussed over at Reddit so can't take credit for this. If you install the Hyper-V feature in Windows 10 on your Surface Pro 4 and reboot as prompted after the install you should now see your Surface Pro 4 enter Low Power mode (DRIPs) during Connected Standby sleep and see a lower drain rate on your battery during sleep. I have tested this and it is working for me along with a couple of other users over on Reddit. It's still not perfect, as although it is now entering a "Low Power State" it is seems not to be able to completely put the SOC into it's lowest power mode which is indicated as a percentage against the 'HW: Low Power State'. So still work for Microsoft / Intel to do!