Honestly, it could mean some really bad things. But as another comment pointed out, they'd need a financial incentive to counteract the bad press. And oh would there be bad press.
Nothing, because ISPs don't care about Bitcoin. They neither profit from it nor incur any noticeable costs.
They could be paid by parties that don't like Bitcoin, though...
I don't think that makes sense either for ISPs or for the third party. ISPs are evil, but they're not cackling supervillain evil.