I have not used the Stonewall(X2) feature personally. From what I understand, most users who mix using whirlpool will mix directly into cold storage. Stonewall(X2) would be more a tool when going to spend the mixed UTXO from the post-mix wallet. It seems that a bitcoiner using Stonewall would also not volunteer this info online or promote it openly (to maintain their privacy/operational security). These are just some of my thoughts, would love to hear what others think.