\setupalign[r2l]
\setuppapersize[A4][A2,landscape]
\setuplayout   [location=middle]

\setupnote[footnote][rule={on,right}]

% \setupnotedefinition[footnote][location=left,width=1cm] % !!!
% \setupnotedefinition[footnote][location=left,command={\smash[w]}] % !!!
% \setupnotedefinition[footnote][location=left] % !!!

\definedescription[testa][location=left]
\definedescription[testb][location=right]
\definedescription[testc][location=inleft]
\definedescription[testd][location=inright]

\showframe

\starttext
    \starttesta{a} \input ward \stoptesta
    \starttestb{b} \input ward \stoptestb
    \starttestc{c} \input ward \stoptestc
    \starttestd{d} \input ward \stoptestd


    Text\footnote{Note}
\stoptext
