The idea sounds quite interesting. Would it be like a full-out war, with all the options and battles, or something different? I have always been under the impression that the feuds were more surreptitious than all-out war. Assassinations, attacks in the woods, etc.
As for implementation, I suspect the coding would be quite difficult (to understate it). I recall back when the intra-realm conflict was discussed (between duchies), it was mentioned by a dev that the coding would be a beast try get right.
