In 2017 ghostscript added support for the /Print and /View keys of the Optional Content /Usage dictionary[1]. The use of '-dPrinted' should display the print-only layer, per the documentation[2]:

gs -o output.pdf -sDEVICE=pdfwrite -dPrinted input.pdf

From their repository you can see that poppler (i.e. evince) also checks the /Print and /View keys[3].

I'm reporting this here since neither render ConTeXt's "printable" viewer layers - not while viewing, and not after printing.