A related thread is http://taleworlds.com/v-web/bulletin/bb/viewtopic.php?t=296&highlight=enemy+heroes which is about Enemy Heroes.
The idea is similar and I like it also.
I suspect we're just asking for more clowns like Borcha and Marnid, but I do agree it adds novelty, variety and randomness. These heroes might be "killable" and if killed, we'd have a simple gravemarker for them we could ride by from time to time on our adventures.