I would love a way to separate the checklist by person. As in, who is responsible for each thing. My groom has his own list and it'd be nice if I could maintain it and easily link it to him, and maybe if he could link an account to mine easily. I haven't seen a way to do that yet. Amazon has it for wedding registry and it's really useful because he can add things if he wants without using my account, yknow? Anyway, I guess a "Honey Do List" would be a nice feature overall as well as a "Bridesmaids do list," maybe with email reminders etc. So that way all the groomsmen can check a page and see the tie I want them each to pick up, and I can tell when they've marked it as done easily.
So maybe more like a hub for keeping track of everybody's jobs, without everybody needing to make accounts or log in.