Getting page numbers in plain TeX

Yes of course you could implement the same system latex uses, with a two-pass writing to the aux file. You could define some macros just to do this or more simply

\input eplain

and use the eplain macros which provide various cross referencing features in a more plain style than the latex macros.

Yes of course you could implement the same system latex uses, with a two-pass writing to the auxiliary file. You could define some macros just to do this or more simply

\input opmac

and use the opmac macros \ref and \pgref which provide various cross referencing features in a more plain style than the latex macros.