It mainly depends on whether customers / patrons will be satisfied with what the finished product looks like.I'm fairly certain we'll see a smooth transition. At some point SS will be close to what DC considers finished, we'll probably see an announcement and a date. Then the patreonpage will change to the new game, SS will be taken off patreon and hopefully get that last "incest update" which DC promised and then work will continue on that new project.
Until now SS is successfull because it's unique, it's good quality, it's pretty much timeless and because DC delivers on a constant level. I don't see why DC's next game shouldn't do "well", too.
Players like different things and satisfying many of them can be too difficult a challenge. Why?
Because the SS already has a large base at the moment. Many NPCs and many women to get. Hence, many stories to tell.
In order to tell the whole story well and that the whole thing is consistent and does not contain logical holes, you still have to introduce many new NPCs which again increases the story.
Many players with such a large base think that they will find what they like best. There is a good chance that many will fail.
At the moment, one can only say that the SS has a very big potential to be a very good game ... but at this pace of development it will either not use this potential or it will be developed over the years.
And such a long development threatens to bored players and the departure of patrons or burnout of someone from the team creating the game.