Speaking from some bad experiences in the area, I wouldn't ignore the multi-threaded issue. It's much easier to incorporate multi-threading from the start than it is to go back and retrofit it later. As an example, Tclblend was originally implemented as a single-threaded app, and I ran into some really ugly problems when I tried to integrate it in with aolserver. In the end, it turned out to be easier to rewrite the core functionality than it was to integrate tclblend with aolserver.
In any event, I can't wait to see how your work turns out. I've always wished that I had a tclsh based interface to openacs. This could turn out to be quite a useful tool in many respects.
