Cross-reference to the next section, whatever it is

We have to setup a \label that will be evaluated at the next \section command.

So I patch \@sect to add a \label command to its argument #8 (which refers to the main section title), which is evaluated only if the command has been called by \section and a \nextsection command has been issued. Also \section and \subsection need to be patched, because they both use \@sect for typesetting the title. The argument to \label is automatically generated via a counter.

Note that the patches must be made before hyperref is loaded.

\documentclass{article}
\usepackage{etoolbox}

\makeatletter
\newif\if@nextsection
\newif\if@section
\newcounter{ns@count}
\newcommand{\nextsection}{%
  \global\@nextsectiontrue
  \stepcounter{ns@count}%
  \xdef\@nstemp{ns@@\thens@count}%
  \ref{ns@@\@nstemp}%
}

\patchcmd{\@sect}
  {#8}
  {#8%
   \if@section\if@nextsection
     \label{ns@@\@nstemp}\global\@nextsectionfalse
   \fi\fi}
  {}{}
\preto\section{\global\@sectiontrue}
\preto\subsection{\global\@sectionfalse}
\makeatother

%%% hyperref should go after the patch, if used
\usepackage{hyperref}


\begin{document}
\section{TL;DR}

This section is long, go to section~\nextsection.

\subsection{A}

\newpage

\section{THIS IS IT}\label{foo}

\newpage

\section{Again TL;DR}
Check if it works \ref{foo}; now go to section~\nextsection.

\newpage

\section{Another}
\end{document}

This answer has been EDITED to work for the next section, the next subsection, as well as the next subsubsection.

In essence, rather that try to invoke a label in one place meant to apply to a subsequent report section, it makes more sense to me to create macros \nextsection, \nextsubsection, and \nextsubsubsection in which the next [[sub]sub]section number is computed based on the current [[sub]sub]section number. It will, however, require you to know in advance whether the next sectioning unit entity is a section, a subsection, or a subsubsection.

\documentclass{article}
\newcounter{nextsec}
\newcommand\nextsection{%
  \setcounter{nextsec}{\thesection}%
  \stepcounter{nextsec}%
  \thenextsec%
}
\newcommand\nextsubsection{%
  \setcounter{nextsec}{\expandafter\parsesub\thesubsection\relax}%
  \stepcounter{nextsec}%
  \thesection.\thenextsec%
}
\newcommand\nextsubsubsection{%
  \edef\tmp{\thesubsubsection}%
  \setcounter{nextsec}{\expandafter\parsesubsub\tmp\relax}%
  \stepcounter{nextsec}%
  \thesubsection.\thenextsec%
}
\def\parsesub#1.#2\relax{#2}
\def\parsesubsub#1.#2.#3\relax{#3}
\begin{document}

\section{First Section\label{s:first}}

This is section \ref{s:first}.  The following section is \nextsection,\\
but the next subsection is \nextsubsection.

\subsection{A subsection\label{s:firstsub}}

This is subsection \ref{s:firstsub}.  The following subsection is \nextsubsection.

\subsection{Next subsection}

\section{Next Section}

The next subsubsection will be \nextsubsubsection.

\end{document}