Do we still need MGF1 as used in the PKCS#1 v2.x specifications for SHA-3 hash functions? MGF1 is currently used for OAEP and PSS as Mask Generation Function. Now that the SHA-3 specification contains SHAKE128 and SHAKE256 could MGF1 be replaced?
It seems to me that there is only one input to MGF1, called the seed. It seems that MGF1 is directly replaceable with a XOF which also has one input and one output. In that case we could call MGF2 = XOF, and the XOF (hash) function would simply be one of the SHAKE functions specified in the SHA-3 standard.
Will a extendable-output function directly cover the security requirements expected from a mask generation function?