The merger of PIO and OCI cards is to ensure uniform rules and extension of benefits to all. Thus, you no longer require a PIO. You can only apply for OCI card or get your PIO card converted. Benefits of merger:
Simplification of rules under a single umbrella;
PIO card holders get additional benefits similar to OCI card holders;
Simplified visa- free entry for people of Indian origin;
5 year rule applicable to all for obtaining Indian citizenship.