I'm looking on if it is possible to use OPML and RSS to display
accounting information.

At http://www.summasummarium.com/morten/accountopml/ you can see an
4 year old prototype using OPML for accounting purposes. Regretably
its still in Norwegian.

I've seen in the RSS 2.0 specification that referring to other
namespaces my allow to extend RSS 2.0. I wonder if I can use this
feature to include OPML.
Since I'm quite inexperienced in RSS, I also will ask if it could be
possible the other way round, include RSS in OPML.

I have recently started a blog (actually my first) noting my
thoughts and observartions at http://cdeaandrss.blogspot.com where
you find more background on my private research.

Sincerly,

Morten Jacobsen