I recall that that was what was suggested for Java's HashMap too, but they found it to be insufficient. By careful analysis, an attacker could still figure out how to cause hash collisions.
I haven't seen those discussions, but is it possible that they were trying to rehash the results of Object.hashCode rather than pass all of the bytes of the original value through a new hash algorithm?
Afaik, they augmented the hash function with a random seed, which didn't work out. See: http://emboss.github.io/blog/2012/12/14/breaking-murmur-hash... It appears that SipHash would be enough (for now) to prevent hash poisoning. Most open addressing hash implementations doesn't yet use SipHash though.