The inserting inline is pretty easy - like you say we just make up a new tag - what is tricky (or will require thinking due to the infinate ways it could be handled) is how these parts will be handled in the ui.
You are right that inso is Oracle specific - we can use vwWare: http://wvware.sourceforge.net/ for word documents and pdftohtml: http://pdftohtml.sourceforge.net/ for pdfs. I am sure we can find other tools for excel etc.
