Fair enough, this is a good point.
I guess the question now is, do they just happen to be closer to release than we think (<2 years), or is it truly going to be several years-long marketing campaign (2-4), and this reveal was just to save their hide?
Tough to say. Probably be easier to draw conclusions once we see gameplay for ourselves.
Well, there was that leak not long before E3 that turned out to be very much true: they mentioned First Person perspective, wallrunning and possible Moon Dlc.
When it comes to DLC, this is almost always worked on, when ( nearly ) all/most main game content is finished, and writers and other teams start to set some groundwork.
Q&A/bugfixing and optimizing will require a lot more than they did with Witcher, though.
So I don't really see anything past late 2020 ( along with clear mentioning that they're definitely planning to release the game for this gen).
They probably seemed to have planned something like Fallout 4 marketing, but scope of the project and public interest possibly changed this.