That seems like a good place for it. Do you need anyone's final approval for this? @zygoloid, any objections to this move?

If we ever want node handles for list and forward_list, we'll probably want it one subclause earlier, but this is fine for now.

We can already splice with lists, and there are none of the problems with keys being const when using a list, so there's little motivation to extract a node in order to muck about with it. If you really want to, you can extract a node into a separate list (i.e. std::list<T>::node_type is std::list<T>)