Based on this:
Nieuwe kleuren, een nieuw budget, maar in deze Tour de Franc
www.indeleiderstrui.nl
I'd say Skjelmose will be up there (incl. for stage results) in the first week, but then fade and have the rest of the Tour be a fight for survival, in order to salvage as good a GC as he can. - Unless he has a complete off day and drops so much time he can hunst stages the rest of the Tour.
So on balance maybe top 20 is more likely than top 5, at this Tour.
I think if he manages a top 10, Trek will be over the moon, and let him prepare as a proper GC captain for next years Tour, to give the overall a serious shot.
If he shocks everyone and manages a top 5, we have a new GC star on our hands.