There is still significant sharing that can be achieved inside a VM, plus, a lot of the sharing come from zero pages (full of 0) which is still performed accross VMs.
Another benefit of the salting mechanism is that it allows the administrator to define groups of VMs that are trusted in which sharing will be performed.
disclaimer: I work at VMware and wrote the salting code.
A lot of those optimizations would no longer yield any benefits[0]. The CPU archictecture evolved a lot in 16 years, especially in branch/code prediction to the point where a correctly predicted branch (without branch_likely) has almost no cost.
Another benefit of the salting mechanism is that it allows the administrator to define groups of VMs that are trusted in which sharing will be performed.
disclaimer: I work at VMware and wrote the salting code.