OK, now that the book is out, does the proficiency listed for katana for the ninja and the samurai cover the exotic (one-handed) use of the weapon or just the martial proficiency (two-handed)?
I'll bet to one handed. Specially because samurai are profient with all martial, and two-handed katana is already martial, no need to specify if not is going to be one-handed.
You are proficient with an exotic weapon since Katana is an exotic weapon. The Katana just has quality that allow it to be used two handed as a martial weapon. There really is no such thing a martial weapon proficiency in Katana because it's not a martial weapon.