Hunting in Linkedin reveals good hints.
Lee Imes (Website): Joined San Diego studio in August 2013. Has Clint Eastwood on his profile picture. His website shows his attempts at modeling Clint.
Derek Payne: Worked in Rockstar since DMA design. Left recently (March). He says: 'In addition to GTA, I worked on UI aspects of as yet unreleased/unannounced titles' (nothing new, but still interesting) .
I can go on and on, but it's easy nowadays to do a Google search (rockstar games unannounced site:linkedin.com) and you will find interesting stuff. This guy for example (LINK) says that he worked on GTA V, Max Payne 3 and an unannounced title during his time in Toronto studio between 2011-2013.
I just hope we somehow stumble upon a profile that precisely lists the title of an unannounced game (Red Dead 3 for example). As far as I remember, There were times in the past when some developers mentioned GTA5 on their profiles prior to its announcements.
Nothing earth-shattering, but interesting nonetheless given the current saturated atmosphere that is caused by GTA Online. A glimpse of hope? light in the darkness? this kind of thing