I mean it would be only optional if people want to go down those extreme road, otherwise, if game keep going vanilla, it would become boring.
The adventure means: an unusual and exciting or daring experience. There are a lot of solutions to continue the game:
A.: one of them is to finish the adventures by some variants of endings (1. summarizing the experiences and ending open marriage, 2. continue the open marriage together, 3. continue the adventures with breaking), and spicing all of them with pregnacy or not.
B.: to continue the game with more unusual, exciting or daring adventures.
C.: to spice up the game uniting it with the gamevariant with the lurking thoughts of the characters, and integrate it with more teasing and refusal during the game. To spice up the character of MC with more passion. Now Anne enjoys her adventures more to MC. Eg. is missing some spontaneous ejaculation of MC during cuckolding or swingigng, generating more passion in Anne, and is missing some double or triple penetration of MC, with multiple orgasm of his partners too, during cheating, swinging or after cuckolding.
It was quite succesful keeping the game going vanilla till now. I think to go down to those extreme roads by your proposal would be the subject of an other game.