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To be honest I wouldn't expect kagerou sai to be a good master. In the past he kinda was the sort to kill kids form what I recall. If he had a disciple and said disciple would make a mistake in regards to the rules he has he would actually kill that disciple. I don't think he has what it takes to be a good teacher. The disciple would last even less if he was as eccentric as kagerou.
You underestimate the eccentricity! Plus he's changed Sai already promised Shigure he wouldn't kill again. What I'm imagining is him dispensing sage advice to an equally strange young weapon enthusiast while he walks around with a hoe attached to his back. As I said he hasn't really shown the inclination, but at the same time he's the only weapon user worth anything. A new weapon user able to merge with his weapon would be out of nowhere, unless its the dude who managed to escape the elder during the akabentou raid.