OP your question has been answered but to clarify - yes, as of right now you will have a date based ticket. No you will not need a reservation to any park. Yes you can hop to another park whenever you want, as many times as you want to as many parks as you want. If you plan on using Disney buses, they don't start running park to park until 10 (as of right now). You could, however hop a bus to a resort that is within walking distance to a park at any time. I think the monorail between MK and Epcot runs all day and does not have the 10 am restriction. I say as of right now because things can and often do change within the course of a year.
As for the other question about someone who has a reservation to park and hopping. Yes, you can still hop, you just have to step foot within the park you have a reservation for then you can hop. I have been known to tap into MK, walk into the front part of the hub for whatever and leave and go to another park. MK on weekends is another matter if you have an AP but we won't go into that. I've found, for the most part, reservations have been pretty easy to change even the day before or day of but I don't go on holiday days such as Christmas Day or Thanksgiving days so those might be the exception. I don't even look at the good to go days situation since I stay on property but they might come into play if you aren't and you can only make reservations for x amount of days at a time. If you stay on property you can make reservations for length of stay. Push comes to shove, you just make a reservation for any park, tap in and hop out to whatever park you actually wanted to go to.
