hopefully. the thing is, RDR is just hard to top. its was fantastic. 

The only element of the old West missing is a huge Native American presence. They could move the series back in time and really focus on conflict between the White man and the Natives. So much they could do story wise.

Current gen RDR would be awesome, there's plenty that can be done there.
Say and show something about Agent, whatever the deal is with that, if it's canceled then put people out of their misery, if not then they must have something to show by now, it's been like 8 years since it was announced.

Maybe a Midnight Club, unless the franchise has been axed?

From other studios at Take Two obviously Bioshock and Borderlands are really wanted by fans.
Plenty of others too.

Give us some surprise like Rockstar doing a futuristic epic, with GTA style humor and epic space battles. Not sure how that would work, but I'd love to see those goes try something completely new.

Maybe an insane Platform game, with epic gameplay!
Make it all Epic!!!!!

A new Red Dead would be incredible. I'll also throw in Agent for the lolz.

When do you think we will hear about this? At E3? or later?

I don't think Rockstar usually throws an E3 stage show, maybe they'll just announce these games through mainstream gaming media or perhaps they'll have their own event to show off new games.

The likes of Agent could be shown off at Sony's E3 event, if it's still around, maybe even GDC, with a Rockstar presence at their conference. If that game isn't a PS4 exclusive, then I think it would probably be Sony that Markets it on their platform.

Overall though it could just be random announcements, as and when these games become ready for Rockstar or Take-Two to unveil the games of their developers, I guess we'll find out throughout this year and in the future beyond that.