I am always looking forward, considering and evaluating how new options/features might be deployed in Core. I cannot say for certain what might be in 5.0 other than some things are being actively coded and evaluated.
As for cpio gziped additional initrds they are for sure not a thing of the past. They are and remain a viable option for loading extra functionality be it modules, as in the example you gave, or to merge additional code into the base OS available at startup before attempting to find and load extensions. Adding startup script capability just adds to the usefulness of the system.
Core being a kit means you have much to consider when "building up" your system. gz startup scripts is one more tool for your consideration.