Could Paul Ryan be in trouble in 2018 if there is a backlash?

[Greedo punched first]

1994 and 2006 would have been impossible if PVI determined everything.

To an extent, 2010 and 2014 too. There were several D+4-5 seats that House R's won that year, not to mention winning high profile Senate races in states like Illinois, Wisconsin, Massachusetts, and Pennsylvania. I think the House is very much in play, and a lot will depend on Trump (though I know that many people on this board insist Trump doesn't stand for most of the Republican Party. Well, I think those Blue Dogs would've said the same thing in 2010).

Incumbents frequently win by a much wider margin than the PVI. Paul Ryan got 65% of the vote in 2016. It's unlikely he loses; unless he makes big mistakes.