I am glad to hear that there is a much interest in implementing a plug-in for drawing diagrams of all kind.

>I already create a Flow-Chart plugin for TWiki, and that
>draws a SVG in the web server before to make the PNG
>to send for the web browser:
>That may be a start...

Interesting TWiki plug-in. Is this plug-in using http://www.graphviz.org/ in background?

>I would also refer to http://www.csse.monash.edu.au/~mwybrow/dunnart/
>and http://adaptagrams.sourceforge.net, both with flowcharting in mind
>and created by Inkscape developers.

This is a great starting point, too. The site not only contains a reference program, lot of papers, theory and references can be found, which is a great starting point to read and learn about algorithms and stuff.

I think it is a good idea to make clear what the goal is, and what the requirements are to achieve this goal. A good way to collect all this information, is to create a new wiki page. Does a such wiki page already exists?
I am just because I just found this in the RoadMap http://wiki.inkscape.org/wiki/index.php/Roadmap#Milestone_18_-_Inkscape_0.52_-_Tech_drawing_abilities

I no such wiki page exist, we can just create it to collect all information: goals, reaquirements, etc.

There are many things to figure out and talk about, before starting to implement anything. For example the user interface: do we want a click&drop interface for the user,
a textual interface where the user just describes the realtionships between elements in plain text, and than inkscape calculates an optimal alignment of the elements and draws them on paper.
a combination of click&drop and textual description.

And not to forget we will a huge database of predefined pattern. On the one hand we need a databse of 'element pattern': a computer-symbol, a people-symbol, a paper-symbol, etc.
But on the other hand we also need 'diagram patterns': a flow-chart pattern, a UML-class-diagram pattern, a workflow-diagram pattern, etc.

We can try to look how Visio solves problems, but we can also have our own ideas to make an even BETTER program then Visio it is. And I am SURE we can just do that.
I have the luck to have a Visio installation on my computer installed, because of a 'Microsoft students software program'. So I can see how Visio does this&that.

So, what do you guys think how we should go on? I am for the plan to first create a wiki page and collect all kind of information: goals, requirements, possible user interface, plug-in architecture, ...
Does anyone can do that?
We will also need some designers to create all kind of patterns. But I think this is no problem, because the InkScape community is a huge one with a lot of designers, too (I guess).