I can report it doesn't work here. And I am pretty up-to-date with GWTeX, although this makes me want to try updating today. This:

% output=pdf

\usetypescript[postscript][\defaultencoding]

\setupbodyfont[postscript,10pt]

\starttext

\input tufte

\stoptext

Gave me this:

(/usr/local/teTeX/share/texmf.local/tex/context/base/type-akb.tex))kpathsea: Running mktextfm utmr8t

mktextfm: Running mf-nowin -progname=mf \mode:=ljfour; mag:=1; nonstopmode; input utmr8t

This is METAFONT, Version 2.71828 (Web2C 7.5.5)

kpathsea: Running mktexmf utmr8t

! I can't find file `utmr8t'.

<*> ...:=ljfour; mag:=1; nonstopmode; input utmr8t

                                                 

Please type another input file name

! Emergency stop.

<*> ...:=ljfour; mag:=1; nonstopmode; input utmr8t