As others have said, thus far there have been no issues with being able to hop. I was there early April, had hoppers and hopped every single day. One day I hopped to 3 parks, not by some plan or design, just happened. Which is what is great about having them, you are able to just go with it.
As far as transportation taking a lot of time, I've never had an issue with it and have always had hoppers and have always used Disney transportation. I walk between HS and Epcot (and no I'm not young and/or fit). AK and MK are morning to mid-afternoon parks for me. I spend part of every single day at Epcot. One of the good things about them is you really don't have to worry about getting anywhere at any special time. Tired of park A and it's after 2 (right now), no problem hop on the first bus to arrive and move on.