First of all u can already have the current version with beta.
Now about ur question there are many reasons, example of few:
1. Majority of ppl disliked it and ppl wont pay for something they dislike (this is a paid DLC so ppl are more sensitive).
2. If he release a disliked content and plan to update it later, its bad marketing.
3. Early sale of a product is its biggest sale time if u ruin it, u wont sell much even when u fix it.
4. U cannot make same content which do same thing CO exist, it does require extra energy, coding, bug fixing, support and is a waste of time for producer overall, SPECIALLY when one is superiors to the other.
5. the updated version is not suppose to remove any of the fap materials, if we assume that with update he is going to add corruption system like waitress or office or strip job, then with high slut lvl u can still have same content as right now, so the current build is absolute.
6. alot of other reasons...
But they always said dlc will be free if im not mistaken, now, what im guessing from their course of actions is that patreon whales didn't like the concept and i can understand that, the real time waste comes from not using all those assets and systems already implemented.
And yes, you can make the content co-exist just fine, they're doing modular coding for their in-game objects, systems and stuff.
Also as you said, if we go by the approach of it being an actual dlc for the game, just read reviews and dont buy it if it sucks, your view would be valid if they haven't already put the work into the system and already made the art.
As for bug fixing, i think if you played the game on the various early access versions, they have handled the bug fixing really fast, i can remember 10 different patches being released on the same day at some point, if you own the game on steam you would just have to release a patch which will would be a small patch.
And as for the Co-existing concept, it really depends on what does he want to do with the rework, for now im assuming he would make a corruption system making karryn end up getting fucked in the showers or something like that, and if he takes that approach, both systems could work just fine, just both sharing the idea of the gym and maybe gym rep or some variables like that.
