Preface: I have not read through all of the thread.
however, the closest thing I can think of for the scenario you propose is to give me, the player, a compelling reason to risk the women i already have in a system that maximizes player agency and challenge.
So for example, you might dangle hot/interesting characters outside the starting 3 as the incentive with the player chasing clearly understood "things" to acquire them, maybe even only temporarily. Those things might be money, connections, drugs, outright removal of rivals, etc. then you offer the player several ways to acquire those things with gambling the main girls as a way to speed up the process or help raise the chance of success . . . the catch being you might lose them.
what you're aiming for is the feeling of being on a knife's edge between success and defeat, or a mastermind trying to hold on to a rapidly unraveling ball of plots, interests, etc. the key, in my opinion, is to maximize player investment in the characters, to build tension, and then make sure the gameplay never hard-locks the player arbitrarily. the player should clearly understand the risk, the player should have a number of well balanced "tools" to modify their risk/reward and "make plays" to reward good understanding/skill, and finally, the player should be able to recover from losing . . . perhaps by taking even greater risk.
leane 2: leane of legitimate crown is almost a good example of this in that you can get good at the army combat game-play, risk your female generals, and the story is compelling. the issue is that it fails to find a way to inform the player about key game mechanics relevant to the NTR before the big twist. so unless you play with a guide it's easy to play a long time, get to the twist half way through, and be utterly screwed into the "avoidable" NTR. It was very much like getting to the end of a 10 hour tutorial only to get an game over because you didn't guess the important mechanics not introduced.
was it a good NTR? probably. Was it fun for anyone that doesn't want to role-play a beta? no, not at all. which is unfortunate because it has a lot of clear effort put into it and is by far one of the better built RPGM games. and what's really unfortunate, is that all the tools were there. it's a game of kingdoms and great battles, but the player is never given the option of changing his lot. no coups, no rebellions, no stealing the crown. without a guide (and what's the fun of always following a guide?) it's basically a hard railroad onto the NTR path that makes less and less sense the further from the, I'll admit, well done mid game twist one gets.
That's the key that most NTR games miss, and why I feel it's so hated. most games with it are a binary. you're either on the NTR path or you're not. There's very rarely the option to flirt with that line and because of that a lot of NTR also fails to really build the tension that's supposed to define the genre: that feeling of being stolen from and watching the whole world crumble down. Without risk and player choice I'd argue you're not writing real NTR because you're not capturing that tension and without risk and player agency the "NTR Haters" will always be fully justified in loudly denouncing the railroading.