A D R:
OK, I have some ideas on this matter but my brain is not really in the mood for ideas at the moment I guess. Maybe this will be something I can expound on later, or not...
Sounds interesting. I remembered some more about it overnight. In Ken's framework (which I think is pretty traditional Karma Kagyu, see e.g.
article on Trungpa's treatment of them), the five buddha families are elaborations on the five elements in the Pali canon, which there is no natural hierarchy to.
I think Ken mentions a hierarchy of increasing rarefication, earth -> water -> fire -> air -> space, which also corresponds to the ascending order of the corresponding chakras. In his
talks at the Warrior's Solution retreat, he did have an ornate preliminary meditation involving successive visualization of each element breaking apart at its chakra and flowing into the next element in the sequence. However, I believe the intention of this meditation is to establish perception of the five elements in empty (Bahiya-style) terms.
If this is interesting to you, he is pretty responsive to email.