Just recently, the gaming world was hit with the bombshell that Grand Theft Auto 6 could feature the series' first Latina protagonist. The report, originally relayed by Bloomberg, said that she was one-half of two playable main characters, which were described as a Bonnie & Clyde-type robber duo. It was also stated that the game would take place in a fictional version of Miami and that it was most likely still a couple of years away. A newsletter from Axios Gaming has now claimed that a source familiar with Rockstar had told them that earlier plans for GTA 6 had it featuring four protagonists and three cities at launch.
GTA V was the first game in the series to feature multiple playable protagonists in the main story, with three; Franklin, Michael, and Trevor. It seemed Rockstar was originally hoping to up the ante and continue to raise the bar with their next mainline entry by having four this time; not to mention having multiple cities in one game, which would increase the playable area for a GTA single-player experience to unprecedented levels. But it would seem somewhere along the way they realized such a goal would be too difficult to reach if they wanted to release the game in a reasonable timeframe.
Therefore, as per the prior report, Rockstar appears to have sensibly tuned it down to two protagonists. However, something vaguely aligns between the two claims, as Bloomberg stated that Rockstar would continually update the game over time with new missions and new cities. GTA V's online mode was a ridiculously massive success; it's the reason it's still heavily played to this day, and it receives a constant influx of updates. It could be that Rockstar wants to implement that model more quickly in the newer GTA and have big updates soon after release for both their single-player and multiplayer audiences.
It could also be that this multitude of cities and protagonists wasn't exactly scrapped but instead left for later to help feed a new content pipeline Rockstar plans to have for GTA 6. If Rockstar wants GTA 6 to have the same longevity as GTA V, launching the game earlier and finishing extra content (like multiple cities) later, would be the best strategy. Were these reports true, the new missions could possibly feature different playable characters.
The number of protagonists is something that needs to be established early during game development, especially in GTA games that have story-based missions which usually heavily revolve around their characters. So, these plans, if they can be believed, are likely from very early production talks. Nothing has yet to be officially confirmed, so right now, the entire gaming community is biting their nails waiting for some sort of teaser reveal that will confirm or deny these rumors.