It's an issue certainly & has been discussed several times. It has to the case that if it ever happens there will be some disappointment, e.g. some don't like the character who pairs up, or were counting on it being someone else. Maybe the circumstances didn't suit them & there's always the fact that some fans won't find it sizzling enough, after all the years of anticipation & the dribbling can of fuel the Dev has poured on this slow burning suburban bonfire. There'll be a barrage of criticism, that's a given, though there will also be many positive reactions. If it ever happens the thread & the Patreon pages would no doubt go crazy.
This is another area where L&P is, to some extent, in danger of painting himself into a corner [he already has IMHO] but such an event would have the positive outcome of a massive increase in interest & a surge in followers, paying & pirating. There might be echoes heard around the web but because of the outstanding fan art in existence, most of us already know what a copulating Sophia looks like & with a selection of partners. Anti-climax, (pun intended), is a sure reaction from some fans. Actual in-game sex would, however produce another potentially interminable, "dangling carrot", in the form of, 'will it occur again with the same person &/or who's next?'
Might I suggest another plausible scenario, namely that we never see Sophia have full sex with anyone outside her marriage, unless we count an existing daydream sequence, plus Antonio of course. People will stop playing the game, whether or not Sophia has sex but the risk of mass desertion after "the act", I believe, is less than the risk of people starting to drift away in ever larger numbers, as the realisation of what is really going on here sinks in.
I could be wrong & hope I am but I can't envision this VN going on for more than a couple more years. When it gets to the stage of 1/3rd of a playable day in 1 year, or more, some might contend that it was past time to abandon this once so-promising story in any case & I mean both the Dev & his fans. Then there would be talk of who could re-do the whole game.....