They can go longer than they have. Especially when each new installment has made MORE than the last. Hollywood never pre-emptively gets off the horse. They certainly don't get off the horse while it still seems to be increasing in speed. They will wait until they release one that doesn't meet their projections. One that doesn't make more than the previous movie did. One that wasn't their top-grossing film of the year. I agree with you that they will abandon the franchise as if it never existed as soon as it ceases to be healthy. But no one at Paramount can be delusional enough to think they are at that point NOW, when all numbers point to a continued up-swing.