It was before possible to interact with ray marching from any shader by simply checking for ray context and then deal ie. with sg->Ci .. as you removed it in favour of closures, - how are we now supposed to deal with that from a generic shader ?
An explicit AiClosureVolumeAtmosphere will have to be on a different shader etc. and for complex (param wise) skymaps for example it would force to layout and setup again all the params initially and then again and again for any tweak done on the skymap, - which is an UX nightmare for end-users.
What you had in mind exactly when you removed that simple workflow ? Can you add something to this if you understand what's the problem ? I say it in this way because last time after months you said you did not understood the question (and not because I wasn't clear enough I think), so now I'm asking, - do you get what the problem is here ? (hint
.. over-engineering vs user-oriented dev).