I wasn't able to specifically find this item on this forum, but post-build 1511 the Surface Pro 4 has excessive battery drain during sleep (like ~10 percent per hour even with WiFi turned off during sleep). The device also is running "hot" under normal circumstances unlike pre-1511.
I had read about this on the web but finally bit the bullet and contacted Microsoft support via chat to work the issue. After extensive troubleshooting, most of what I had already done, the agent finally acknowledged the following towards the end of the chat (even though I had specifically asked the question at the beginning of the chat):
ME:Are there reports of this issue in your knowledge base?
Microsoft Agent: Yes we have it in our knowledge base and I would like to assure you that we are aware of it and Microsoft is currently in the process of developing updates that will fix this issue. We are to release new updates that will enhance the performance of the device specifically with the battery.
Me: When is the fix expected?
Microsoft Agent: We don't have specific date yet but I will personally monitor it for you and will send you follow up emails about it. I'm gonna make sure that you'll be one of the first valued customers who will get this update once it's available.
Further, the overheating issue was confirmed to be related:
Me: One more thing -- we didn't discuss the fact that the device gets far hotter than usual, but my research show that is a result of the battery issue we've discussed. Is that true?
Microsoft Agent: Yes that's correct. Since the battery consumption is not normal than before, it affects the fan to run faster and release a heat.
So this is at least a formal, now written acknowledgement of the issue, something that is only hinted at in various sources on the web.