There definitely are access points that From built into the game for those areas that are coming via DLC, but they were scrapped for various reasons. There presence in very early concept art shots confirmed that they are old assets and not newly created content. From doesn't operate on that model of build now, release later via dlc. Similar to how to the broken archstone. It's quite possible they had content for that but scrapped it due to it not fitting in with the overall game.
The use of time to explain inclusion of the new content also points to a method of including content that did not fit within the context of the world. Coupled with knowing that From is already working on a new game, it stands to reason the DLC production team was headed by Namco engineers.
Regardless, even though I may come off as pessimistic regarding Namco's intentions of the new stuff, I do agree that any content From has a hand in is better than 99% of what's out there