Even if it were promoted to interstate status, keeping the number 152 would be very unlikely. After all, California hasn't used up all its x38's yet. Signing errors are a popular topic on misc.transport.road , and California is not alone. Connecticut, for example, updated a big green sign for US 5 and CT 15 with the markers switched, giving state route 5 and US 15. Posting to misc.transport.road, Aug. 25, 2000.
Unnamed sources are either maps or personal experience.