User blog comment:Lordbryan123/Saji and his future balance breaker/ pawn peices/@comment-1359322-20130928145159

Well the Evil Piece becoming Mutation Piece is a hidden featured placed by Ajuka, so it is possible that there are also other Evil Pieces aside from Issei's became the same.

As for Saji's Balance Breaker, i guess or hoping that he'll get 4 Balance Breaker and another one where he combines all four. Since Yuuto's 2 Sacred Gears are of opposite nature so they can't be used in tandem but Saji's Sacred Gears are from the same source, Vritra, so it should be possible for the Balance Breaker to coexist.