There's no mention of what it could be except that Xbox One and PS4 releases are likely, with PC hopefully included. It's possibly the long-awaited Agent, once a PS3 exclusive.
The trademark for Agentby Take-Two in July 2013. Very little has been released about the game except it focused on 1970s Cold War espionage.
Grand Theft Auto V and GTA Online is another major on-going project at Rockstar Games with a PC version in the works but with no official announcement. It is believed they will re-release GTA V for Xbox One and PS4 at some stage, which has sold over 33 million for Xbox 360 and PS3.
Recently Rockstar San Diego’s Red Dead Redemptionin Microsoft's Windows Compatibility Center.
Rockstar Games has made no mention of appearing at E3 this year, which is something they've missed for a while claiming they prefer events specifically tailed to their announcements. Take-Two's fiscal year ends March 31st, 2015.