Ironically this whole thread played out in the opposite direction at the time of SHA3's announcement:

https://www.schneier.com/blog/archives/2012/10/keccak_is_sha...

https://www.imperialviolet.org/2012/10/21/nist.html

tl;dr: Keccak is not a good partner for PBKDF2. It has good hardware performance but comparatively poor software performance. This benefits attackers with FPGAs or better.