plan.org puts a compiler-provided, type-directed println at milestone 5: a structural printer selected or emitted per concrete instantiation, Ptr printed as an address rather than followed, depth and length bounded. That is a description of the renderer C-x C-e already has - same walk, same refusals, the same three bounds - pointed at flan_dev_emit and the wire instead of at stdout. Recorded next to the renderer so it is not built a second time. What println needs on top is a stdout sink, a builtin that takes its printer from the argument's type, and the any/Error cases, which have no compile-time type to walk.
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