Was at the Kaigi and on the opening keynote Matz talked a bit about it. He doesn't really support adding it since he feels like in 20/30+ years, advances in technology will make writing types "obsolete".
My take is he doesn't really like (or "get") types and feels protective of his language, which is fair. I think Python made an interesting choice here, i.e. provide syntax for types without semantics. The drawback there is potential fragmentation on type system semantics.