Performance sorta hinges on it. It could be that the cheaper way the chipmakers deal with it is to phase out the 4core set and push the cores on a die higher,

Performance sorta hinges on it. It could be that the cheaper way the chipmakers deal with it is to phase out the 4core set and push the cores on a die higher, and to do that--incorporate an older core design into dedicated cores for untrusted code. This would also require changes at the OS-makers to tag thread forks for trusted and untrusted behavior. Essentially: instead of shutting down SMT for the entire machine, make the customer "prove" the code is safe for elevation or else it gets scheduled as non-SMT.