First of all, Gao's conjecture was that there does not exist a super square balanced set in a Finite field. Square balanced sets are known, in fact, Gao himself, in his paper, given an example of a family of square balanced polynomials.
There has been some additional work in 2008, by Chandan Saha and he gave an algorithm for factorization that works for all polynomials except a restricted class called cross-balanced polynomials. The conditions required for a polynomial to be corss-balanced appears to be stronger than super square balanced.