Some say a pvp vendor, but it will probably be irrelevant after a few expansions as you move to different main hubs unless Blizzard is committed to moving the NPC.
My suggestion: A portal in the main portal hub for both factions that takes you to a neutral dueling area with a pillar in the middle, and the pillar is Reckful himself. Either him IRL or his character in game, with a plate carved with his name at the base of the pillar.
This is not only something that would be cool for Reckful. But even people would like an official dueling area for both factions in the same place to help with numbers. Also, it would be a nice bonus to have all arena modifiers applying in that place to encourage people to duel there.