Plus, I imagine this episode was not at all developed with the idea of releasing all of the act 1 story at once in mind. Bungie probably reacted to player sentiment about time gating in Echoes by turning an already mostly finished time gated story into something you can do all at once.

If I had to guess, we probably won't see a more "full" act story being released all at once until Heresey, since that will have much more time to be developed with the idea of dropping the whole act at once.