\documentclass{article}
\usepackage{tikz}

\makeatletter

\def\pgftransformlineattime#1#2#3{%
  \pgfgettransformentries\pgf@tempaa\pgf@tempab\pgf@tempba\pgf@tempbb\pgf@notimportantx\pgf@notimportanty%%% ⬅️⬅️⬅️ new
  \pgf@process{#2}%
  \pgf@xb=\pgf@x% xb/yb = start point
  \pgf@yb=\pgf@y%
  \pgf@process{#3}%
  \pgf@xc=\pgf@x% xc/yc = end point
  \pgf@yc=\pgf@y%
  \pgftransformshift{\pgfpointlineattime{#1}{\pgfqpoint{\pgf@xb}{\pgf@yb}}{\pgfqpoint{\pgf@xc}{\pgf@yc}}}%
  \ifpgfresetnontranslationattime%
    \pgftransformresetnontranslations%
  \fi%
  \ifpgfslopedattime%
    \advance\pgf@xc by-\pgf@xb%
    \advance\pgf@yc by-\pgf@yb%
    % Now that we get the tangent vector without transformation
    % It suffices to apply the non-shift part of the transformation
    {%%% ⬇️⬇️⬇️ new
      \ifpgfresetnontranslationattime
        \pgfsettransformentries\pgf@tempaa\pgf@tempab\pgf@tempba\pgf@tempbb{0pt}{0pt}%
        \pgf@pos@transform{\pgf@xc}{\pgf@yc}%
        \global\pgf@xc\pgf@xc
        \global\pgf@yc\pgf@yc
      \fi
    }%%% ⬆️⬆️⬆️ new
    % OK, now xc and yc are correctly tangent to the line
    % Continue the usual routine
    \ifpgfallowupsidedownattime%
    \else%
      \ifdim\pgf@xc<0pt%
        \pgf@xc=-\pgf@xc%
        \pgf@yc=-\pgf@yc%
      \fi%
    \fi%
    \pgf@x=\pgf@xc%
    \pgf@y=\pgf@yc%
    \pgfpointnormalised{}% x/y = normalised vector
    \pgf@ya=-\pgf@y%
    \pgftransformcm%
    {\pgf@sys@tonumber{\pgf@x}}{\pgf@sys@tonumber{\pgf@y}}%
    {\pgf@sys@tonumber{\pgf@ya}}{\pgf@sys@tonumber{\pgf@x}}{\pgfpointorigin}%
  \fi%
}
\makeatother

\begin{document}
\begin{tikzpicture}[xscale=2, yscale=3, xshift=40, yshift=50, nodes={above}]
    \draw (0, 0) -- node[sloped] 
      {\texttt{sloped} only} +(2, 2);
    \draw (2, 0) -- node[transform shape] 
      {\texttt{transform shape} only} +(2, 2);
    \draw (4, 0) -- node[sloped, transform shape] 
      {\texttt{sloped} and \texttt{transform shape}} +(2, 2);
\end{tikzpicture}%
\end{document}