At this point I think it's quite safe to say that Red Dead Redemption 2 will be delayed. If they wanted to release it this fall then they would have been giving us news and updates at this point. My guess is that we are probably looking at a spring or fall 2018 release instead.
If that's the case then there will be a 5 year gap between RDR2 and their last major release which was GTA V in 2013. R* said in a Q&A session that they "have so many games that they want to make but the issue is always one of timing and limited bandwidth".
The question is if we will have to wait another 5 years after RDR2 is released for their next major game. Then it has to be GTA VI because there has been a 10 year gap (!) since the last installment in the series. And like they said themselves, it's about timing. It can't go too long for a game in a franchise to be released because then players will probably lose interest.
But the question is how can Rockstar have time to make any other games than GTA and RDR with this current release schedule that they have? I know that these are their two best selling franchises, but Rockstar has always been known to take risks and try to make something new.
I hope that they have used these 5 years to develop other games simultaneously with RDR2. But I'm not sure since it seems like all their studios and employees are working on it.