A package I've been involved with lately is fset, which is available through quicklisp, or at

https://github.com/slburson/fset

It has some interesting features, including "functional setf expansion". This would turn something like

(setf (fcar x) y)

into something equivalent to

(setf x (cons y (fcdr x)))

(where "fcar" and "fcdr" are the same as "car" and "cdr", except when they are in a setf-able place form.)

(fcar and fcdr are not in fset; I used those names just for exposition here.)

It could work with nested accessors, but only if it bottoms out in a variable.