A good idea except for one issue, that group can then all get in another line elsewhere and get a FP that nobody else can get. If there was a way to prevent them from getting in other lines it would be great.
But that's pretty similar to the way old paper FPs would work. You'd send a runner with all the paper admission media while the others would go do something else. In my case, it was often something I didn't mind missing, or because I could navigate crowds like a New Yorker, I'd often catch up with them before they made it to the next line. Or, because we'd try to go when crowds really were light, there'd be plenty of walk-ons, like IaSW, where no one cared if I went through to join others because the total wait for everyone was under 5 minutes. This last scenario apparently doesn't exist anymore, and my legs aren't what they used to be, but I've been there enough that I still wouldn't mind sitting out a ride in order to get passes for the group. Think ordinary restaurant, where one person goes to get a pager while the others browse the mall.
Nevertheless, I still see the advantages to FP+, at least for those groups who simply don't have someone capable of running across the park to pick up passes in person.