Hey all, following up on my question in #2307, I implemented the following feature:

Ctrl+shift+LeftMouseClick on the pdfViewer copies to clipboard the mouse coordinates x and y in cm with respect to the bottom left corner of the page. This is useful to add floating elements (especially in beamer presentations) as in the following example:

\documentclass{beamer}
\usepackage{tikz}

\tikzstyle{float} = [overlay,remember picture, shift=(current page.south west)]

\begin{document}
		\tikz[float] \draw (0,0)  grid (16,10);
		\tikz[float] \node at (8.6955,4.32964) {\Huge a}; % this coordinate was obtained by ctrl+shift+click on the pdf and ctrl+v here
\end{document}

It's already working in the commit b7e0e9b.

Let me know if there is interest in merging this.