Deterministic keys with one-way operation BIP 0032 "Security Implications" states


  One weakness that may not be immediately obvious, is that knowledge of
  a parent extended public key plus any non-hardened private key
  descending from it is equivalent to knowing the parent extended
  private key (and thus every private and public key descending from
  it).


From what I understand, the weakness is due to the reversible nature of the operation on extended public key (addition). Wouldn't it be possible to address this by using a one-way function like hashing instead of addition?
If you use a one-way hash function (ie like hashing ECDSA public key with SHA256/RIPEMD160 into a hex public key) then how can you employ hierarchical deterministic functioning?

You can't. The whole point here is that if you lose your private key for a grandchild public key you can get it back again with the parent key. A two-way hashing function obfuscating the data would work but that's basically what's already in place.