It's not so much the amount of games it's going to span, it's the amount of console gens it's going to get released across.Remake came out the same year the PS5 dropped and part three will likely release in 2027 on the 30th anniversary of FF7. Hamaguchi recently been talking a lot about part three so I wouldnt be surprised if we get a trailer at the game awards.
Started in the PS4 gen, will probably wrap up in the PS6 gen.