I generally try to stay away from VNs that this new. In fact, I generally just search through completed stuff, but that leaves much to be desired. I hate waiting, especially when we're talking about months, or even years. I think, that this, however, is going to be worth the wait.
The premise is great. In terms of two siblings banging, this doesn't stretch suspension of disbelief too far, and the characters don't simply gloss-over the f-ed up-ness of what they've done and what they're doing. To me, the more the story and characters acknowledge this, the more interesting it is.