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And cdr-coded lists, or sublists, can have vastly improved cache performance, especially when you have a transporting GC.

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Does any implementation updated in the last 25 years use CDR coding??

I don't know -- most implementations on popular architectures only have two (low order) bits for tagging due to alignment issues, so there may not be room. Might be easier in the case of a RISC V with the tagging extension.

Also it would be possible to implement such an approach in a C++ list container where you don't need boxing (the content type is known).

On a 64-bit machine where everything is aligned to two words (like SBCL), you get 4 bits for tags.

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