Based on the order the light hits the planets in the ending cutscene we have Mercury (CoO), Mars (Warmind), Reef (Forsaken), Dreadnaught (?), then eventually the pyramid ships.
My guess is D2 Year 1 is CoO and Warmind, D2 Year 2 is Forsaken, D2 Year 3 is Savathun/Dreadnaught and then Destiny 3 will start with the invasion of the pyramid ships. Gonna be a while until anything about them comes to light (pun intended)