The PS4 iteration of PS2 Classics could be in the works, as a trio of the legacy hardware's titles have been rated by the Pan European Game Information Board.
Gematsu reports Twisted Metal: Black, Ape Escape 2 and Dark Chronicle (Dark Cloud 2 in the US) have been rated on PEGI's New Games” list for PS4 release.
PS2 games have been available on PSN for a long while now, just not via Sony's current generation console. Twisted Metal: Black has been out in Europe as a PS2 Classic for PS3 since September 2013, for instance.
The report points out Sony is holding this year's SCEJA Press Conference in Japan this week. Perhaps we'll get an official announcement.