At the end is there really an issue with the scene?, is there really a need to make it optional? It could have been just something that happened and because branching is expensive that would just be how the story goes
The issue is mostly the context surrounding it. The easiest fix would have been to just have it made clear Rika was not looking for an exclusive relationship. The choice stating it would be is the issue along with the way the story had been shaping up to make it look like an exclusive relationship.
The scene was used for 3 reasons. 1. Make a reason for the wolfman form. 2. Have a reason to use the witch again. 3. Hint a little at the player's history.
Realistically if a monster form was wanted for the game then it should have been part of the reason the player is needed to fix the situation. Have breeders have a trait which allows them to transform into monsters allowing for them to breed safely and could have been a method to increase the stats of the player character.
Start with no knowledge of the trait so only "safer" monsters can be bred initially which is why the financial situation is bad. Then either the trait is found and the witch is searched for or the witch is found and then the trait is discovered. Ingredients are need for the potions to unlock forms/strengthen the player if only one form is used.
This then can still tie into the player character's history and possibly be the springboard for a storyline looking into their past.
Going back to Rika now after talking about the 3 reasons the scene was made. We go right back to the exclusivity relationship after the scene and we continue to still push that way. Even before the rework we still had that happen. If she wanted to just experience fucking monsters and not have an exclusive relationship then just letting her into the pit and having flashback scenes to her time in the past would have worked well.
When the scene had been made I had chosen to let her fuck other monsters assuming she would enter the pit and did not care either way for scene as the context of it didn't go against what I stated. I initially was annoyed with her trying to be monogamous partner for the player because it did not make sense to me with how her character was initially positioned. I had barely been paying much attention to the story at the time and was wanting to see the gameplay evolutions of the game.
Going back over the story multiple time because of complete loss of save files or corruption of files has made me focus more on the actual storyline structure which shows multiple issues of taking up ideas, going one direction for one specific scene and then dropping the idea to get back to previous status quo [aka your bitches only fuck you].
Another example of status quo is the elf village. All it leads to is another monster type to fuck and an NPC which only fucks you. There could have been vendors and mechanics which update gameplay or lead into other storylines. Maybe some form of automation which could allow for difficulty to scale up or allow new mechanics to take a forefront. Instead it is a single monster type which can only be donated and a single NPC you fuck once. Yes, I know Cece's pregnancy storyline is tied into this and that you have a scene with Talia but neither have changed the course of the game's story or changed the main gameplay loop we have had since day one.