First of all, I think the author won't care if someone takes it and makes a continuation, because he certainly won't come back to it. I think you are safe... If it will be a properly done continuation
Second, I think you could just call the project something like: "What if?" and make it an "alternative" story. A story that would simply be a continuation of the original one.
So, someone with good skills in story writing and great skills in 3D modeling should be interested to even think about it. But even if someone with the above skills says "fuck it, I'll do it", you have to think about things like:
a) Will this person or a team of people be truly capable of doing it the way it should be done, which means satisfying the fans and the original author?
b) Will this person or a team be even capable of finishing the project?
The chances are close to or equal to... 0. Sadly.
Screwing up a), b) or both could mean that you're deep in the ass as a developer of future vn's - that's a bonus.