As far as I can tell, from the specifications under 8. Uploading Figures to the PLoS Manuscript Submission System a special package for flushing images to end of the document does not seem necessary:

Moreover, figures need not be numbered by section. They should be sequential, as stated under 3. Titles and Legends:
Titles and legends (captions) for main figures (i.e., not Supporting
Figures) should be included in the main article file, not as part of
the figure files themselves. Figure legends do not need to be uploaded
to the online system. Do not include author names or the article title
within the figure files. Instead, list the following information for
each figure at the end of the article file, after the references, but
before any tables:
- Figure number (in sequence, using Arabic numerals: Figure 1, Figure
2, Figure 3, etc.)
- Short title using a maximum of 15 words. The figure title should be
bold type, using sentence case ending with a period (.). For example:
Figure 1. Adaptation and its potential costs.
- A detailed legend of 300 words maximum can follow the figure title.
Each panel should be described in the legend.
With this in mind, I would create a macro/command that would do exactly the what is stated above and merely place them at the end of the document. Here's an example:
\documentclass{article}
\newcommand{\newfig}{% A new figure
\bigskip% Big skip between figure legends
\refstepcounter{figure}% Increment counter for correct referencing
\item \bfseries Figure~\arabic{figure}.\ \ignorespaces%
}%
\newcommand{\figlegend}{% An accompanying figure legend
\item[] \mdseries% Typeset in regular/medium font
}
\begin{document}
\section{First section}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer lacinia nisl ac augue
vehicula blandit. Donec quis nulla at massa blandit aliquet sit amet id mauris.
Figure~\ref{fig:first} is here. Ut et pharetra risus. Morbi hendrerit rutrum magna, eu
porta magna imperdiet in. Proin blandit placerat justo, non blandit nisi dapibus vitae.
Nunc sollicitudin volutpat ante, ac mollis neque ultricies eget. Fusce eu dolor vitae
tortor feugiat sagittis et et neque. Figure~\ref{fig:second} is here. Pellentesque odio
enim, imperdiet egestas suscipit in, accumsan eu nisl. Nunc iaculis semper viverra.
Aliquam erat volutpat. Aliquam augue massa, gravida sed placerat ut, facilisis a ante.
Suspendisse consectetur porta convallis. Fusce auctor lacinia lobortis.
\section{Second section}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer lacinia nisl ac augue
vehicula blandit. Donec quis nulla at massa blandit aliquet sit amet id mauris.
Figure~\ref{fig:third} is here. Ut et pharetra risus. Morbi hendrerit rutrum magna, eu
porta magna imperdiet in. Proin blandit placerat justo, non blandit nisi dapibus vitae.
Nunc sollicitudin volutpat ante, ac mollis neque ultricies eget.
Figure~\ref{fig:fourth} is here. Fusce eu dolor vitae tortor feugiat sagittis et et
neque. Pellentesque odio enim, imperdiet egestas suscipit in, accumsan eu nisl. Nunc
iaculis semper viverra. Aliquam erat volutpat. Aliquam augue massa, gravida sed
placerat ut, facilisis a ante. Suspendisse consectetur porta convallis. Fusce auctor
lacinia lobortis.
\section{Last section}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer lacinia nisl ac augue
vehicula blandit. Donec quis nulla at massa blandit aliquet sit amet id mauris. Ut et
pharetra risus. Morbi hendrerit rutrum magna, eu porta magna imperdiet in. Proin
blandit placerat justo, non blandit nisi dapibus vitae. Figure~\ref{fig:fifth} is here.
Nunc sollicitudin volutpat ante, ac mollis neque ultricies eget. Fusce eu dolor vitae
tortor feugiat sagittis et et neque. Pellentesque odio enim, imperdiet egestas suscipit
in, accumsan eu nisl. Figure~\ref{fig:sixth} is here. Nunc iaculis semper viverra.
Aliquam erat volutpat. Aliquam augue massa, gravida sed placerat ut, facilisis a ante.
Suspendisse consectetur porta convallis. Fusce auctor lacinia lobortis.
Figure~\ref{fig:seventh} is here.
\clearpage
% Figure legends
\begin{itemize}
\newfig First figure caption.\label{fig:first}
\figlegend Legend for the first figure.
\newfig Second figure caption.\label{fig:second}
\figlegend Legend for the second figure.
\newfig Third figure caption.\label{fig:third}
\figlegend Legend for the third figure.
\newfig Fourth figure caption.\label{fig:fourth}
\figlegend Legend for the fourth figure.
\newfig Fifth figure caption.\label{fig:fifth}
\figlegend Legend for the fifth figure.
\newfig Sixth figure caption.\label{fig:sixth}
\figlegend Legend for the sixth figure.
\newfig Seventh figure caption.\label{fig:seventh}
\figlegend Legend for the seventh figure.
\end{itemize}
\end{document}
The above example has references to figures interspersed with all the figure legends at the end of the document (after \clearpage
). No additional packages are loaded. Two new commands have been created: \newfig
and \figlegend
each of which are used in succession at the document end to produce and typeset the list (in the form of an itemize
environment) of figures and legends.

I am assuming, to echo your original comment, that the journal lays this out themselves in order to make sure submissions comply to their standards. Moreover, then they have control over allowing image views in an online version of the article.
figcaps
package? The package doesn't allow (or issues a warning with)\tableofcontents
,\listoffigures
and\listoftables
, but this is probably fine for journal submission.figcaps
if it works for me, for the purpose of the current submission.