This. Totally this. I could never find someone with the same reading speed (especially in English) as me, and I really see myself in the situation you just described, whatever the language the VNs are in.
However, in my case the language barrier makes the experience impossible. My wife (yeah, don't hit me) isn't really fluent in English and, even if she would mostly understand the text we would read, she'd take too much time for me and I'll lose patience after 5 minutes. Even in French our reading speeds are different and the result would mostly be the same.
So while the idea isn't bad per say, it believe it's really difficult to find the autospeed that suit two people perfectly. It would even be easier, as with real books, to read the same VN at the same time but on two different screens and agreeing to wait for the other after each chapter to discuss of what has been read and move on.
I'll stick to vostfr anime, personally.