It's good to reduce the cache hot best case time of course but isnt the more fundamental sin of RC in the extra read/write memory traffic, cache footprint and cross core cache line ping pong when incrementing object refcount fields.
(or if going with BRC, correspondingly there shouldn't be a advantages for this custom CPU feature)
According to information released when the M1 came out: retaining and releasing an NSObject takes ~30 nanoseconds on current gen Intel, and ~6.5 nanoseconds on an M1