No text=none in TikZ?

If you don't need the text then it shouldn't be there anyway. Either you enlarge the node with minimum width,height,inner sep etc. or you can use the text opacity key comfortably.

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\node[text opacity=0,draw=red,fill=yellow!25] (a) {Text};
\end{tikzpicture}
\end{document}

If you also need some placeholder for a text, you can go slightly esoteric and get the width depth height info beforehand e.g. just for the width;

\begin{tikzpicture}
\pgfmathparse{width{"Text"}}
\edef\mywidth{\pgfmathresult}
\node[minimum width=\mywidth pt,draw=red,fill=yellow!25] (a) {};
\end{tikzpicture}

you can use \phantom{Text}

\documentclass{standalone}
\usepackage{tikz}
\begin{document}

\begin{tikzpicture}
\node[draw=red,fill=yellow!25] (a) {\phantom{Text}};
\end{tikzpicture}
\begin{tikzpicture}
\node[draw=red,fill=yellow!25] (a) {{Text}};
\end{tikzpicture}

\end{document}

If one wants a true “phantom” text node (i.e. no selectable text in the resulting PDF) and doesn’t want to manually provide the \phantom macro, one can use one of the following solutions:

1. Using the undocumented keys execute at begin node and execute at end node one can use the lrbox environment (or manually with \setbox) a box which is then used inside \phantom:

   execute at begin node = \begin{lrbox}{\pgfutil@tempboxa},
   execute at end node   = \end{lrbox}\phantom{\usebox\pgfutil@tempboxa}
   

   This works very well for one-liner nodes and also (I assume) for multiparted nodes. Problems arise when the text width key is used because the needed minipage environment is setup outside of the stuff that is given to execute at begin/end node. (Obviously, we could just mimic this ourselves with a minipage and things from TikZ’ original setup).

2. After TikZ puts the text between { and } in a box it checks the values of the keys text width, text depth and text height and corrects the box measures accordingly. After transformation, the node is created via the \pgfnode macro. We can intercept this here with the following setup (and a little help from etoolbox):

   \usepackage{etoolbox}
   \patchcmd\tikz@fig@continue{\tikz@node@transformations}{%
     \iftikz@node@phantom
       \setbox\pgfnodeparttextbox\hbox{%
         \vrule height\ht\pgfnodeparttextbox depth\dp\pgfnodeparttextbox width0pt%
         \vrule height0ptdepth0ptwidth\wd\pgfnodeparttextbox}%
     \fi\tikz@node@transformations}{}{}
   

   This would simply overwrite the \pgfnodeparttextbox with rules that are exactly the width, height and depth of the original \pgfnodeparttextbox (just as \phantom would do).

   Personally, I prefer this solution, combined with the following keys/conditional, that also provides (besides the text=none syntax) a key phantom.

   \newif\iftikz@node@phantom
   \tikzset{
     phantom/.is if=tikz@node@phantom,
     text/.code=%
       \edef\tikz@temp{#1}%
       \ifx\tikz@temp\tikz@nonetext
         \tikz@node@phantomtrue
       \else
         \tikz@node@phantomfalse
         \let\tikz@textcolor\tikz@temp
       \fi}
   

3. Another option can be used with the upcoming version of TikZ which provides a node contents key. We can create a key that takes its argument and passes it to node contents encompassed in a \phantom. This will only work for one-liners.

   Phantom/.style={node contents=\phantom{#1}}
   

Code

\documentclass[tikz]{standalone}
\makeatletter
\newif\iftikz@node@phantom
\tikzset{
  phantom/.is if=tikz@node@phantom,
  text/.code=%
    \edef\tikz@temp{#1}%
    \ifx\tikz@temp\tikz@nonetext
      \tikz@node@phantomtrue
    \else
      \tikz@node@phantomfalse
      \let\tikz@textcolor\tikz@temp
    \fi,
  Phantom/.style={node contents=\phantom{#1}},% only CVS, only single line
  PHantom/.style={
    execute at begin node=\setbox\pgfutil@tempboxa\hbox\bgroup,
    execute at end node=\egroup\phantom{\usebox\pgfutil@tempboxa}}
}
\usepackage{etoolbox}
\patchcmd\tikz@fig@continue{\tikz@node@transformations}{%
  \iftikz@node@phantom
    \setbox\pgfnodeparttextbox\hbox{%
      \vrule height\ht\pgfnodeparttextbox depth\dp\pgfnodeparttextbox width0pt%
      \vrule height0ptdepth0ptwidth\wd\pgfnodeparttextbox}%
  \fi\tikz@node@transformations}{}{}
\makeatother
\begin{document}
\tikz[nodes={draw, text width=2cm}]\path
  node[green]        {Text text text text text text text}
  node[PHantom, red] {Text text text text text text text};
\foreach \iframe[evaluate={\iframe=\iframe/10}] in {0,...,10}{
\begin{tikzpicture}[nodes=draw]
  \node[text=none] (source)                  {Text};
  \node[phantom]   (target) at (2,2)         {Text};
  \node[gray]               at (1,1) [Phantom=Text];

  \path (source.center) -- node[pos=\iframe] {Text} (target.center);
\end{tikzpicture}}
\end{document}