That would spoil the plot though, wouldn't it
Viewing post in A Suggestion to NSFW Devs?
Is not that easy. A game can take you for Dom/Sub paths for certain characters, other will only have a dom or sub paths... tagging with an "Only dom content" or "Only sub content" might not be accurate for some games (for example, mine, where you switch off between those two).
But I can understand the frustration of a player looking for dom content, only to find the MC is a sub (I tend to write more to the sub part, but I'm working on that and making my next storyline balanced between those two), I added a part on my FAQ section in my game description addressing that. If the game includes BDSM or content that features dominant/submissive behavior, it should also include a little description about this.
No, it really wouldn't. Dom/sub content isn't a plot twist, it's a basic part of the premise. And even if it were used as a plot twist, this is the sort of thing that deserves a big warning label both on the website and inside the game. Hiding this sort of thing in what looks like a "vanilla" NSFW game is equivalent to hiding porn in a kid's game. Don't do it.