Yesterday was such a surprise. I think the comments from the team etc. that this wasn't planned in any way are a bit suspect.
You don't learn at the end of a stage how to sit on the top tube and pedal at 50 mph. That was clearly practiced.
No secret that this year Tour organizers did not want Froome to lock things up early, so added a couple of DH finishes to climbing stages. IMO, he and Skye looked at this, and said, hmmmm, we may have an idea here for a bit of a surprise.
In any regard, it made for some rare excitement. I personally LOVE that, for a change, time was gained in the GC ranks somewhere other than a climb or TT!