There's also a recurring theme in all the interviews after release, they were very open about their biggest regret being how much content had to be cut from the original plans for the first game due to budget constraints. Some things were restored in the content packs afterward, but other things were too foundational to the game's overarching structure to make sense to be patched in after the fact. The Dreamer sanctums were going to be full fledged dungeons with a big climactic boss fight with each Dreamer, the Abyss was going to be an entire zone with multiple bosses rather than a plot only area, the Coliseum was going to be part of a much more involved sidequest, and there were several major zones that just didn't end up in the game at all. The result was still a great game, but a shadow of the absurdly ambitious project they envisioned starting out. I assume they're making Silksong with the intention of not leaving any "what might have been" things.