documentclass[10pt]{memoir}

usepackage{lipsum}
usepackage{etoc}

makeatletter
newcommandimmaddtocontents[1]{{%
   letprotect@unexpandable@protect%
   immediatewrite@auxout{noexpand@writefile{toc}{#1}}%
}}
makeatother

%Add Rule to Contents, Write Immediately, Will Replace With Image Later
newcommand{ruleincontents}{%
    immaddtocontents{nobreaksmallskip rule{3in}{1mm}par}
}%

begin{document}

frontmatter
tableofcontents

ruleincontents{}

mainmatter
chapter{Chapter 1}
    section{Ch1, Sec1}
        lipsum[1]
    section{Ch1, Sec2}
        lipsum[1]
    section{Ch1, Sec3}
        lipsum[1]
chapter{Chapter 2}
    etocsettocdepth.toc{section}
    etocsettocstyle{section*{Local~contentsname}}{}
    localtableofcontents*
    section{Ch2, Sec1}
        lipsum[1]
    section{Ch2, Sec2}
        lipsum[1]
    section{Ch2, Sec3}
        lipsum[1]

clearpage
appendix
    ruleincontents{}
    chapter{Appendixes}
end{document}