Mirai just sold 2 sango kaku that have been on their own roots for over 40 years. Ryan also mentions on the stream that he has a big one in his nursery that he plans on air-layering. I would plant it in the ground, and wire some movement into branches you plan to air-layer. Beware, in the ground, they do grow strong, so keep a close eye on the wire, coral bark with wire scars don't heal well.