I don't know, but I'm gonna guess there's a character called Scarlet that will show up (or has already at some point). Given it's a DLC, there's a good chance it might be content similar to the shark-girls and others like Blueberry, Cotton, and Caramel. I wouldn't for sure plan on that but if the same pattern is followed, that very well might why. Then again, it could just be that Alorth wanted to make separate content for folks willing to show more support with an additional purchase. It's hard to say.
Or, as you suggest, that could be the name of the DLC (as a code word for loli stuff or w/e). Anyway, he's basically saying that the new version will be compatible, so if someone has that DLC there won't be a problem with keeping it with the game (probably just via copy-paste into the /game folder or something).