[gsg]

Yes, this has been done a few times. CDR-coding was a hardware-assisted method of unrolling a Lisp list (complicated somewhat by the need to support mutation of car and cdr) that appeared on Lisp machines, and there's a Appel/Reppy/Shao paper on unrolling linked lists in the context of Standard ML.

There's also some interesting work on flattened versions of arbitrary tree structures: https://engineering.purdue.edu/~milind/docs/ecoop17.pdf