I think your desired behavior is wrong. You'd like the inner body of a once-only definition to be like this:
`(let* (($x o$x))
(+ ,$x 1))
But the macro user would write that body as `(+ ,$x 1), with the backquote and everything, and you don't have that backquote in your hypothetical expansion. What you're probably looking for is:
`(let* (($x o$x))
,`(+ ,$x 1))
Or, more accurately:
`(let* (($x o$x))
,(progn `(+ ,$x 1))) ; listing all the expressions in the body
Sorry, that's all the time I have to look at it right now. XD
Also, this isn't much of a response to the "generally hard" topic (except to prove this example takes more thought than I've given it so far :-p ).
