Rockstar is trying to fix GTA: The Trilogy, in fact, the last update fixed more than 100 issues, further they are expanding the world of GTA Online. In the meanwhile, GTA VI should be a thing in some years, and Red Dead Redemption after the success of the second entry, is going to continue.
According to the profile of one developer of Rockstar, Red Dead Redemption 3 is already in development:
It is not a surprise that Rockstar is working on Red Dead Redemption 3. The question is, when will be able to play it?
On another subject, one rumor published some weeks ago stated that Rockstar could be interested in a remaster of Grand Theft Auto IV to current systems and PC for 2023.