I heard a joke somewhere that sel4 is even more successful than Linux because it is running below ring 0 in every Intel chip shipped in the past N decades, plus probably many others.
Intel used a version of Minix rather than seL4 for its Intel Management Engine. [1] There was some controversy about this because they didn't give Andrew Tanenbaum proper credit. [2]
Such a dumb technical choice driven by stupid managerial considerations. They do this ring -1 shit because hardware companies view this as a cheap way to add value. But they don't open source it or contribute back because they view it as secret sauce. Minix as a result didn't get the investments that GPL software receives. Now the project is in hard legacy mode.
