Can't co-sign killing them off. They are definitely old school but the quintessential Stan Lee creation, IMO. They are the very embodiment of Marvel in the 1960s, for all the good and bad that stands for. That's why their powers and origin is hokey.
They were one of the first comic books I remember reading as a kid. My elementary school had a couple of Marvel collections in the library and I remember checking out the one FF collection they had all the time.
There's really not much that can be done with them though. I'm tired of hearing about all of the FF relaunches. They need to go away for awhile. They don't need an ongoing and can be background players and make cameos in big events or bring in a new team and let the original FF people spin off into different groups for a few years.