Here's one possibility: the idea is to \let the font attributes you don't want to use in the list to be, for example \rmfamily (for font switches) or \textrm (for font commands with one argument); this is done \AtBeginDocument using \addtocontents{lof}{...} so the redefinitions only have effect for the LoF.
To change the separation between the number/letter and the title for subfigures in the LoF, you need to redefine \l@subsubsection (for article) or \l@subsection (for book, report); this redefinition has to be done before loading subcaption; then, you can redefine it again, to restore its original meaning for the ToC, if you want to.
\documentclass{article}
\makeatletter
\renewcommand*\l@subsubsection{\@dottedtocline{3}{3.8em}{2em}}
\makeatother
\usepackage{subcaption}
\captionsetup[subfigure]{list=true}
\makeatletter
\AtBeginDocument{
\addtocontents{lof}{%
\let\sffamily\rmfamily
\let\scshape\rmfamily
\let\textbf\textrm
\let\textit\textrm
}
}
\renewcommand*\l@subsubsection{\@dottedtocline{3}{3.8em}{3.2em}}
\makeatother
\begin{document}
\tableofcontents
\listoffigures
\section{Test section}
\subsection{Test section}
\subsubsection{Test section}
\begin{figure}[!ht]
\centering
\begin{subfigure}{.5\linewidth}
\centering
A
\caption{{\scshape test} \textbf{subfigure}}
\end{subfigure}%
\begin{subfigure}{.5\linewidth}
\centering
B
\caption{another {\sffamily test} \textit{subfigure}}
\end{subfigure}
\caption{A figure with subfigures}
\end{figure}
\end{document}
