I believe FP+ will change park hopping, perhaps even make it easier if you are able to get "good" FP+ selections.
Let me take the most obvious example using TSM and Soarin'. Both attractions often have 2-hour plus Standby queues. If you are able to get an afternoon or evening FP+ selection for (for example) Soarin', you could visit DHS for opening and ride TSM first thing (before the line grows too long) and then later hop over to Epcot and use your Soarin' FP+ selection there, without having to wait in too long of a line for either attraction.
The key is to get FP+ selections during the afternoon or evening for attractions that typically develop long Standby queues.
I've played with the numbers believe only about 1-in-4 Epcot guests on a typical day will be able to get a "good time" for Soarin'. The percentage is similar for TSM. Like ADRs, it will be important to book your FP+ experiences early.