A feature similar to what is offered in Inkscape in terms of font export in figures for subsequent pdflatex/latex use would be a great addition to tikz and pstricks I think. We would then be able to draw all our diagrams/schematics/sketches with these great tools including text, store them as pdf files (without text) and then include them in the main file for compilation with respective text tags. Fonts would then be treated in live during compilation thus avoiding the compilation of all the diagrams/schematics/sketches over and over... Change in fonts in the main document would be easy as well. Does it make sense?
I will talk about TikZ since I don't know much about PSTricks, most points will probably apply to both though.
It does not make sense to me. The main (if not only) benefit seems to be the ability to change the font without having to re-compile the diagram. Since a lot of diagrams will have elements which will look different and even be positioned differently depending on the text inside (or even besides) them, I don't see how this would work (See the example below). If you want this to be limited to only text outside of nodes (TikZ talking here) then you would get mixed fonts and the advantage over just including the pdfs vanishes. If all you want is to have the TikZ pictures in separate files you can have a look at the
The example I mentioned above, consider the two following nodes generated by the exact same code, only the first uses Computer Modern, where the second uses Utopia, the resuling image is different.
You can imagine that when other elements are positioned relative to these nodes, the image will look very different depending on the font used. By making the text longer, the difference will accumulate and eventually the text would overflow or the box would be far too large (depending on the direction of the font switch). All in all, I don't think the separation between text and the rest of the diagram elements you propose is feasible. The typesetting of the diagram will always be influenced by the typesetting of the text inside of it.