> That looks like more of a combination of existing monads than a truly new monad.
Well sure, but if we're going to exclude those then the grandparent's ask is a bit high: either we present something useless and pedagogic, or we present something useful that exists in a library somewhere, or we present something new and useful... that we should then also put in a library somewhere!
I must admit that I can't remember ever creating my own monad from scratch.