You can hop if your ticket includes hopping, but you won't have FP+ available at the new park. This means that some people may now want to say go to Epcot at rope drop to hit up Soarin' and TT in standby, but then use their FP+ in DHS in the afternoon for TSM, RnRC, and ToT.
I am not too crazy about the 3 FPs in one park thing either. It's great if you are staying there all day (which I do most of the time) but should we have a day where we are hopping, we should have the option of using those FPS somewhere else. You are given a limit of 3, which is fair, but you should be able to use them where you wish.
For example, next week I will be in Disney for the Halloween Party (a very short Wednesday night to Saturday get away). On Thursday (the day of the party) I plan on hitting up Epcot for the morning till about 12 where I will have lunch around 11 and then head back to the hotel to rest and change for the party in MK. So that only leaves me with about 4 hours to spend in Epcot. For fun, we tested the FP+ stuff, found out we HAD to choose 3 rides there and the way the times fell go like this:
9am Spaceship Earth
10am Journey into Imagination (which really needs no FP)
11:15am Maelstrom (the only ride we wanted to do FP wise)
that leaves me with barely anytime to do anything. Just arrive to make our forced FP slots and get out of there. Though it may not be the case when we are actually there, for now it feels so close together and stressful.
I don't like the idea of wasting FPs, we were originally going to have Soarin' at like 1:45...would not have used it and the FP would have been wasted. It would feel a lot more free if we were able to just choose Maelstrom and then use our FPs on something in the MK later on.
Anyway, I am giving Disney the benefit of the doubt. It's a new system and I am sure there will be changes down the road.