totally forgot about del potro. could be a threat, I think.
i wouldn't discount isner that easily. wimbledon isn't as low bouncing as, let's say, halle.
Only for Nadal and Djokovic. Del Potro's movement on grass is far from ideal and he can't deal with the low bounce, expert slicers like Fed and Murray would most definitely slice him to death if they met imo.
Isner has never made past R2 in this tournament, he really doesn't do well in low-bouncing surfaces. But I guess that when you have a serve like that, you're always a threat. And yeah, the bounce isn't as low as Halle, that's for sure.