Well, after a long call to the Microsoft Support Chat line, the tech concluded that I too should go into the Microsoft Store and have my SP4 swapped - and she had made sure they had a 'better device' for me.
I went in today with no great confidence. The tech in the store was helpful, and went through the checks - firmware installed completely, up-to-date Windows Updates etc ... Having found nothing, spoke about the situation. The tech clearly wasn't surprised,
and I think had seen it before. They were very cautious in the use of words about it, but did admit that there was a known problem in this area, and that I should expect a big update - maybe at the end of March / April.
It felt as though the tech knew exactly that there is a known issue here, but was not at liberty to say anything specific. They don't want to admit it publicly due to the impact in the press.
I can understand the position, but it seems short-sighted and destined to undermine customer faith and loyalty.
This must be a tricky problem, otherwise I would have expected a fix, they do have some smart people working for them after all.
What I would really like is an interim measure, which implements a simple sleep mode, and leaving all this connected standby stuff to be fixed when it can be. Other suppliers have gone for the simple sleep mode on Skylake - and they work fine.
I will stick to hibernate rather than sleep, and now will turn off the Surface Pro 4 when I travel. I flew yesterday with the Surface apparently hibernating, but it turned itself back on after a couple of hours of travel, and it was noticeably warm in my
bag - and with a much depleted battery. I don't think the power button was knocked, but maybe it was that.