That's the way I see it too, well written Beard'.
I can see the business side of it to keep evolving, keep coming out with new models and new rules and constant updates. Which, I wouldn't put past GW in the interest of generating ongoing revenue each year. But I don't think they'll be able to keep the process indefinitely and will eventually settle on a new edition released to set all changes in stone. I feel these individual army releases are addendums/updates leading to a larger compilation text. At least, that's what I'd hope for.
I for one, have always like games with narratives and running campaigns with purpose. I think WHFB is a rich environment where stories can unfold and great scenarios made. I know I've had a lot of fun with Storm of Magic and now the prospects of End Times.