PFS is valuable largely in stable, small groups that rarely change shape or association.

PFS in an open, freely-associable environment is far more complicated when you move beyond even the smallest of group sizes. Realistically, once the group size is beyond Dunbar's number you can reasonably assume that PFS is moot, because you no longer can depend on maybe four or five people's personal security, but 150+. Statistically, someone's opsec failure will be guaranteed.