Given the history of CPU hot plug, it has always been generally assumed that all the CPUs in an SMP are identical (hence the S in SMP). I'm not aware of any OS

Given the history of CPU hot plug, it has always been generally assumed that all the CPUs in an SMP are identical (hence the S in SMP). I'm not aware of any OS that supports differing feature sets, and if one exists, it almost certainly goes with the least common denominator feature set.