Forgive my lack of knowledge on RVSM, but why would a 5th Pod affect the aircrafts RVSM capability?
Probably, no effect - it simply hasn't been tested to see if the presence of the extra engine affects the airflow near the static ports. As 5th Podding is a relatively rare event, I don't think that any airline is going to foot the bill for Boeing to do the necessary test flying for RVSM approval.