An interesting point that I read suggests that not everyone will get the same options for FP+. The system will generate a selection for you, which could be based on which hotel you are staying at, on site or off etc. It may not include all the rides. This is the only part the worries me as there are only a few rides in certain parks I would want to FP such as TSMM, but you will not automatically be given a choice of all. Interesting to see how it will work.
I suspect this is a misunderstanding (not yours!) or rumour based off what someone has heard about the current system.
The way it works at the moment is you select 3 attractions you want from a park and then the FP+ system will give you 3 ready made
groups of FP+'s.
For example if you wanted Soarin', Test Track and Mission Space the FP+ system might offer you:-
A) 9:15-10:15 Soarin, 10:35-11:35 Test Track and 12:10-1:10 Mission Space
B) 11:30-12:30 Soarin, 1:35-2:35 Test Track and 3:20-4:20 Mission Space
C) 5:45-6:45 Soarin, 6:55-7:55 Test Track and 8:00-9:00 Mission Space
You then
have to select one of those options. BUT, after you've selected an option that's closest to what you want (all morning, all afternoon, all evening unless something like Illuminations is offered), you can then go back and amend the times (or even change your mind about the experience) to something else you'd prefer.
Presumably this is done to try and disperse guests who are fairly flexible with times to go at quieter hours. I honestly don't think there's any way that people won't get identical choices of FP+'s unless ofc the time slots are already filled.