The PIO card does exist, and is deemed valid for travel to India (by Indian immigration authorities) until some time in 2020, at which time all PIO card holders have to convert their PIO cards to OCI cards. (This is something that has been repeatedly pushed back by the Indian government, so who knows, the deadline may move and PIO cards may continue to be valid a lot longer.) However, there is a bigger practical problem with the PIO card in that it is not a machine-readable document (at least most of them) and therefore airlines will often not accept it as a valid travel document. If you can convince the airline it's valid, then it's fine to use it for entry to India.