Also, based on this discussion, I understand that combining modes and tabulate is not possible. Instead modes must be comined with natural tables.
A logical follow up questions is if itemize can be combined with natural tables that include modes like in the MWE below.
\startsetups [table]
\setupTABLE [start] [frame=off,rulethickness=0pt,offset=0pt]
\setupTABLE [column] [1] [width=4cm,align=flushleft]
\setupTABLE [row] [1] [toffset=5pt]
\setupTABLE [column] [2] [width=4cm,align=flushleft]
\stopsetups
\enablemode[test]
\starttext
\bTABLE [setups=table]
\bTR \bTC Item 1 \eTC \bTC Column 1 \eTC \startmode[test] \bTC Column 2 \eTC \stopmode \eTR
\bTR \bTC Item 2 \eTC \bTC Column 1 \eTC \startmode[test] \bTC Column 2 \eTC \stopmode \eTR
\eTABLE
\stoptext