Numbers
Will Apple change Numbers so that you can reference one spreadsheet from another? If yes, when? If not why not?
Mac Pro
Today: no. MacOs and iOS are two completely different Operating Systems. These two Operating Systems manage the files (= Numbers documents/"spreadsheets") in a completely different way. External references from one document ("spreadsheet") to other documents ("other spreadsheets") cannot be supported, if Apple wants the Numbers functionalities to be compatible in both Operating Systems, MacOs as well as iOS.
Tomorrow: maybe (if e.g. Apple drops MacOs and keeps iOS).
Paul.