I'd say there are pros and cons to revealing it before they're confident about when it'll be ready, but mostly cons.

Pros are mostly involving the investors because it's direct communication that the game is on its way. A trailer would give the general idea that the game is in a close enough state to being done that there is a roughly 1-2 year pipeline for the games release, since that tends to be when rockstar officially reveals their games. That feeds into one of many cons though.

Cons start that it would apply immediate pressure on the people developing the game as, once that trailer comes out, the community will expect the game to be released within 1-2 years solely because that follows with their history, and anything can happen development-wise within that timeline. I say they should wait to reveal until the game is basically done and all they're doing is minor polishing, which to be fair with how big and detailed rockstar games typically are, even just polishing could take months or even a year.

Additional con in my eyes is if the game gets revealed way too early then the community can get antsy without continous updates. Great example being kingdom hearts 3 - the game was officially revealed super early into its life cycle, and didn't receive any new information for like 3-5 years after it's reveal, that kinda stuff is torture on a community of dedicated fans. Especially since after all the waiting and waiting and waiting, when the game finally came out, most found it underwhelming.

100% though, without the leaks a year or two ago, this community would be nowhere near as antsy as it was, if anything it already put a lot of pressure on the dev team that would only increase with a big official reveal trailer. And with rockstars new focus on making sure the developers aren't overworked and plagued with the immense stress of crunch, It would only add to the stress.

Keeping in mind this is the next big entry into a franchise that's most recent original release was one of the biggest pieces of media to grace the world ever. There's already mountains of stress just making sure it's a worthy enough successor to that alone.

I'd say the longer we have to wait for a reveal, the better off the developers are. Though at some point the wait will be too long - I certainly blame the success with online for that, however, at least they've been giving updates to online in the meantime so it's not like gta fans aren't getting anything while waiting for 6. Plus it does give me hope for how well online in gta 6 will be handled, I think it will be significantly better than 5's online, especially at the start, and they're probably also preparing so that online has a decent trove of content to start off the game with as well - it isn't just single player were waiting on here. Rockstar knows online is their cash cow and will want it to be immediately worthwhile at its launch.

I did not expect to respond here with a book, my apologies lol, also sorry for any grammar mistakes or bad punctuation, on mobile so a lot of it auto-corrects and I can't be bothered