GTA Online content has been released for over ten years. The rhythm tells you something.
The pattern
Rockstar usually puts out major updates twice a year. Minor seasonal updates come once a month. Patterns have shifted over time - heavier towards business updates in mid-life, and criminal-coded updates later on.
Total shipped: hundreds of cars, dozens of properties, multiple major heists and several map expansions.
What this implies for GTA 6
Likely the same cadence on the online side. SP content is harder to predict - GTA V didn't receive story DLC despite years of rumours. Whether GTA 6 will differ from that remains unspoken.