That's going to happen for 100%. DC already talked about his new game several times and has very concrete plans. That said, they'll certainly have to get the timing right, so as many patreons as possible will stay. I'd personally guess that they'll announce the new game at some point, they'll tease a bit, SS will get one or two more updates. SS gets taken from patreon and is replaced by the new game, DC will release the last SS incest update on his homepage and after that the new game continues on patreon.
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Alfius:
Yes and no. DC promised to bring the incest back once the game is done but right now there's no support for any patch and thus there's no easy adaptation for mods. Thus there's no and there won't be official support for those patches and they are fan made.
I've personally never used any of those patches and for me the game is still just as playable as before. Maybe that's because I'm playing it for so long that the relationships are clear anyway.