Now you're out of the realm of Ki, but what you're talking about is still being worked on in the modern era, by me! I'm building BABLR which is a modern follow-up to your idea, built on top of a powerful, generic system of parsers which has gaps/holes but no error recovery, so that it works with trees which may be incomplete but which must not be invalid.

The hard part is that we need to be able to talk about these structures. Even just here on this forum we need to be able to communicate precisely about them. I often use · as a typesetting symbol so that I can easily write and read expressions like 2 + · which you would read as "two plus gap". The · symbol is only for typesetting as I say thought because you it's not safe to assume that any one character is reserved for our use in every programming language. Instead we wrap the parts that aren't syntactic in quotes and we use <//> as the symbol for a gap so that it looks more like this:

  <*> "2 + " <//> </>

The * there is a flag on the node, it means this node a leaf of the tree -- a token.

We can parse 2 + · into a proper tree now:

  <BinaryExpression>
    left: <*Number "2" />
    #: " "
    operator: <* "+" />
    #: " "
    right: <//>
  </>

And yes, BABLR can really parse this. If we've piqued your curiosity, our Discord server is currently the hub of our community and we'd love to see you. https://discord.gg/NfMNyYN6cX