RDR had not been out long (relatively speaking) before Rockstar officially announced the release date for GTA V so it is reasonable to expect that the corporations involved in these two games might try and recapture that lightning in a bottle again for the remaster and GTA 6.
Take Two's stock price has been steadily gaining since the beginning of 2023 and I expect the company has a desire to really put on a blitz ahead of GTA 6's release. That means fans may see some movement on a GTA IV remaster as well.
Rockstar has made it pretty clear that they see their games more as a type of "James Bond" movie event and less like how they did games in the past by churning them out at a more frequent pace. That said, I don't think they wanted it at this slow of a pace. I think that the pandemic likely caused a massive delay in production. Also, creatively speaking, I remember one of the Houser brothers seemed sort of... stuck... when he commented that America is becoming impossible to parody in the present time.
GTA Vice City and San Andreas worked really well in this regard because they rolled back the time a decade or so and held up the mirror to that not-so-distant time. IV and V pulled away from that and things got a lot more serious. "6" appears to be in that same vein.
Oh, the remaster. Let's hope this happens. There appears to be quite a bit of evidence out there that it will happen soon enough. It's never really been in doubt to me that it would, just a matter of fitting it in around 6 and the pandemic. The sloppy remaster of III, Vice City, and San Andreas might have helped RDR in the long run. The game deserves a lot of attention and would be a fabulous experience if it used RDR2's engine.
UPDATE: RDR was not "remastered" using the RDR engine. That said, it was released for Nintendo Switch and the PlayStation, both of which it was not previously available for.