\setupbodyfont[dejavu]

\definefiller[test][alternative=symbol,symbol=!]

\starttext

dummy \page

\testfeatureonce{1000} { % 0.19  | 0.60
%     \setbox0
        \hbox to \hsize
            {text
            \removeunwantedspaces\leaders\hbox to 1em{\hss !\hss}\hfill\ignorespaces
            text}
}

\page

\testfeatureonce{1000} { % 0.27 | 0.65
%     \setbox0
        \hbox to \hsize
            {text
             \filler[test]
             text}
}

\stoptext
