Top 5 this year with Mark Freaking Sanchez starting 6 out of 10 games. Foles was an INT machine to start the year too and can't stay healthy, which is why they are even contemplating doing this in the first place.
I think Mariota will work out better with Chip for the Eagles than RG3 did with Washington - just look how RG3 did when he had a real offensive coach in Shanny. Just gotta hope they get completely milked on draft picks in compensation (and no, McCoy will not be part of the deal, he is owed $10M next year, no bottom feeding team wants to take that on for a 26 yr old RB when they likely have much bigger problems).