Does Yone's triggered ability trigger when he holds in Reckoner's Arena, even though the battlefield isn't empty (since he's there)?

Ruling: Yes, Yone's ability triggers when holding in Reckoner's Arena because the Arena's "activate" effect puts the triggered ability onto the chain directly, regardless of whether the trigger condition (empty battlefield) is actually fulfilled.

Nuances:

• Normally, Yone cannot conquer an empty battlefield if he's already at that battlefield, since his presence makes it controlled/occupied rather than uncontrolled/empty
• With Skyfall of Areion (which makes his conquer effect a hold effect), Yone's ability would NOT trigger because the battlefield is not empty when he holds
• Reckoner's Arena specifically bypasses the normal trigger condition check by using "activate" wording