Thanks for all your comments!
Sorry that I didn't provide much information. The idea is to have a specific 'confusionplot'-function
that takes care of label issues and such stuff, creates an appropriate dataset, and, than just calls 'imshow'. 
You're absolutely right, keeping all features of 'ConfusionMatrix.plot()' requires working on the interface.
I'll write 'confusionplot()' next, try to preserve old functionality, see what gets lost and than we have to
try to get it back...