[skissane]

In principle, you can save the same amount of memory with CDR-coding.

In practice though, you run into some issues (1) RPLACD/set-car! makes CDR-coding much more complicated (I suppose you can just ban it – in Racket, pairs are immutable by default, although there is also a separate mutable pair type); (2) CDR-coding generally only works if you construct the list up-front, the existence of CONS can encourage a coding style in which you don't do that; (3) to fix (2), you can force the list to be CDR-coded by duplicating it, but you have to remember to do that at right points – if you don't do it, you'll miss out on the benefits of CDR-coding, but if you do it when you don't have to you are unnecessarily harming performance; (4) since CDR-coded and non-CDR-coded lists are the same type, and indistinguishable without peeling off the covers of the implementation, it makes it harder for the programmer to address (2) and (3) correctly.