Is sussokan as you teach it widely spread in the Rinzai Sect or is it limited to a certain lineage or lineages? What is the reason you place much emphasis on this teaching?

Sussokan is not being taught in a zendo. Is is said that the Zendo is a place of only deepening your mind by meeting your own limits. Getting to know yourself. Hakuin Zenji got sick from too intense practice and with his compassionate heart he taught Sussokan.