We don't know how it's going to work, and everyone is making assumptions about the one hour.
I would imagine they are modeling this much like the
DAS system which totally incorporates the standby wait time into the return times. The computers automatically determine the times and attach it to the digital pass.
It could be that the system will be set up to be standby time plus one hour. That would give a party plenty of buffer if they use the standby line and WAY plenty time if you utilized the FP+ line. Just a guess on my part but it would make much more sense than giving someone a flat one hour return time, especially since many of these rides SM, 7DMT, FoP, FEA, RnR etc can be close to an hour or even more rendering the pass completely useless.
All those that were overusing and abusing the GAC were upset with the new DAS. Disney was still offering a fair and generous option for those folks with disabilities who needed it. Folks had gotten use to the above & beyond usage. I think this will be the same .... Disney doesn't actually have to offer anything at all in terms of rider swap, they could leave it totally to the guests to figure it out ... but they are still giving folks an option for a second adult/party member to ride without a long wait after they babysit someone.
And as I've said before, Rider Swap came about before there was ANY FastPass. With FastPass they actually could have dropped the program altogether. They didn't, it got out of control and they are doing what they need to do operationally to keep the program.