\addff is for adding some feature to an already selected font. It fails in the latest beta's because fonts are no longer preloaded immediately, but only after \starttext (which is a good thing)On Mon 11 Apr 2011, Khaled Hosny wrote:
...(\addff is meant for temporally applying font features not the other wayaround, but I think it should work this way too, so may be somethingis broken)
\addff{oldstyle} works with my 2011.02.25 ConTeXt, so evidently it's
quite a recent change.