I think it handles all the 3VL problems I've encountered in SQL, but that doesn't mean it handles all possible 3VL problems. It also might not make any sense to anyone except me.
It's been a while since relational algebra so I don't feel confident saying "Yes" or "No" (I guess you could say my reply is Null) - but that seems like a really good base approach - especially having a state for being uncertain whether something is nullable or not... having an operator embeded fallback approach also seems to be a lot more usable for the developer.
Also, this is an aside, but is your thing named after Snake Plissken?
Yeah, kind of. I have seen Escape From New York but I don't really remember it. I was more aware of the character via the reference/homage in Metal Gear Solid 2. In any case, I don't love the name but the obvious choice (Racquel) was already taken and "Plisqin" had zero Google results so I said "meh, good enough."
Also, this is an aside, but is your thing named after Snake Plissken?