Agreed, except I am hard-pressed to think of any project in any field that took more than a few months where an early design goal didn't pan out....
Implementation is the constant sad process of hard realities sanding down the idealized dream of the design goals.
As a software developer, we were always incredibly careful to not share early design ideas too soon or with too broad an audience. It's what we always referred to as "whiteboard goals", things that come up in discussion that would be kind of cool and, at first glance, seem reasonable. Because it doesn't matter how much you qualify things with "we would like to" or "what we're currently planning" far too often it gets turned into "you promised" accusations.
I'm sure at some point they thought that after initial release they would provide additional modules if they still had jobs (which at a certain point was questionable). Then the game started growing by double digits almost immediately surprising everyone and it wasn't necessary.
That, and tying it back to the thread, significant modules would have effectively meant multiple editions of the same game. It's bad enough now with some people using feats, some not, what supplements you're using not to mention house rules and 3PP. You can only have so much variation before it starts to feel like different games and leads to confusion and frustration.