You shouldn't get your hopes up about any impending GTA-related announcements.
Despite the domain having been registered all the way back in 2009 - over a year after the release of GTA 4 - some suggested it was related to Rockstar's reportedly in-development next GTA. The crackpot theory goes that Rockstar is looking to pull a Capcom and title the next game GTA VIce City, with the VI here representing 6.
Of course, none of this has any basis in reality. The more likely explanation for the domain's existence, given when it was registered, is that Take-Two could have simply wanted to ensure ownership should it ever need it. Publishers do this all the time to secure domain rights for potential game names, expansions and the like, even without a game actually existing.
Though this practice can be costly, it is much more preferable to having to bargain with a domain squatters who are likely to ask exorbitant prices to let go of a domain.