The jit engine complains

    lua error       > error on line 12 in file
    C:/Users/rik/Desktop/junicode_bold.tex:
    C:/ConTeXt/tex/texmf-context/tex/context/base/font-otp.lua:192:
    invalid value (nil) at index 1 in table for 'concat'

and produces an incorrect document (no bold or bold italic fonts used) 
for the following document, while the standard engine produces a correct 
document without complaint:

    \starttypescript [serif] [junicode]
       \definefontsynonym [Serif]           [file:junicode]
       \definefontsynonym [SerifItalic] [file:junicode-italic]
       \definefontsynonym [SerifBold] [file:junicode-bold]
       \definefontsynonym [SerifBoldItalic] [file:junicode-bolditalic]
    \stoptypescript
    \starttypescript [junicode]
         \definetypeface [junicode] [rm] [serif] [junicode] [default]
    \stoptypescript
    \setupbodyfont[junicode]
    \starttext
    \fontalternative{\it\fontalternative}{\bf\fontalternative}{\bi\fontalternative}
    \stoptext

I also note that the standard typescript for junicode is not useful. 
Beside mentioning goudysans (a cosmetic issue only, I think) the font 
file names do not reflect current file names for the font as available 
at http://junicode.sourceforge.net. If anybody has a typescript 
reflecting current ttf file naming, I would appreciate receiving a copy, 
either via the list or directly.

(The typescript in the above is stripped to a minimum, and not what I 
would use other than in such an example.)

-- 
Rik Kabel