Sorry about your food.

So many thoughts...
Good news is that it doesn't have to be only incest, you can get the risk elsewhere. A supposedly secluded place which turns to be less secluded than expected, in a park, school, ... It's slightly different risk, but also good.
I don't like this one, it assumes that just because she fucks person / animal / vegetable / mineral / whatever, I'm somehow better and would be preferred option if available, which is simply not true.
I'm all for other fetishes. Like good-shaped cucumber, no doubt about it, I see it as creative solution to a problem. Well, not that much creative, it's kind of obvious. But it's perfect for shy and horny girl, who doesn't want to go out and fuck first guy she meets. I'd take a game anytime, with female NPC like this and MC who needs to find a way how to approach her (not so simple, she'd be horny, but not easy) and win her heart (I'm hopeless romantic).
Hell, even dog is fine, if we take out the real-life stuff like being unhygienic, etc. It's not for most people, but strictly in fiction, it's higher level of creativity, it's no longer just thing, it's beloved pet, there are some feelings, it could make good story. It's unlikely to happen in any game, because a) most people are disgusted by it, b) Patreon, Paypal & friends won't allow it, so it would have to be someone's non-profit project, c) pretty much all works on the subject I've ever seen are more or less parodies, with ridiculous plots, elephant-sized dogs, etc, so it would be miracle if it suddenly changed.
In a way, I'm still 13.
Hey, as long as it's optional, it's fine. For me, at least. The problem with NTR is that too many people have too strong feelings about it. Some love it and won't be happy until big black (preferably) guy ruins MC's loved ones forever (I don't understand that). Others are overly sensitive about it, even the slightest possibility that it might happen is enough for them to say "no thanks" and go away, often in less polite way (I don't understand that either). Nobody is going to touch Sarah in my game (I hope, I'm at your mercy), but for some paths it might make sense and if it's avoidable, I don't see a problem.
Patreon is being stupid. Unfortunatelly, it's still the best platform for ongoing support. And it's most likely not from their heads anyway, the whole world (almost) seems to have more and more trouble undestanding that fiction and reality are not the same. So yeah, probably not worth the risk now.
Yep, it makes sense. But it's not so hard to leave it to player's imagination. Not everything needs to be spelled out. Just don't make it clearly contradicting. I for one wouldn't need "sister" in each sentence, her name is better anyway, more personal. Of course some parts could benefit from hints about the relation...
Reality is troublesome. But it's not mainly the incest itself, it's more the other things, abuse, etc. Not that incest would be commendable or anything, but there's no need to go overboard against it. And reaching into fiction to fight it is plain stupid.