I know I keep saying it, but J Rod is coming.
With such a technical course Froome might struggle to put in massive time (edit, although he has reconned the stage). If Sagan finds his climbing legs (tired or resting yesterday?) he could go well given his handling abilities. Should be an exciting TT, good chance of rain showers throughout the day.
The theory is that Froome's descending is only good if he's following a quality wheel. Hence why some expect him not to shine today. I'm not sure myself...
Personally I think Costa might do it again today.