I love to have a duel/sparring option and it could work in this game. To be honest, I was suprised that this option was not included when they started adding PvP to this game. I think these options would make it very viable to have a duel/sparring option:

1. If players dont want to duel, they have a option that automatic will block people from sending them a invite. Alot of people dont want to be called names for not wanting to duel, but we should understand that the players that insult others for not wanting to duel, are the same type of players that will insult for every silly thing. These type of players are small and loud.

2. Make certain locations a NO PVP zone. There will be no PvP near cities, quest hubs and when a Hunt spawns, there will be no PvP allowed near it. Alot of players are saying that they are bothered by the skill effects that will happen during a duel. But how is this any different from a player fighting a monster next to you and spamming alot of skills?

3. Dueling should not give any reward, its only meant to practice/duel with another player so you can test yourself against players or test out a new rotation with a player that will adapt. I think dueling is a great way to practice and improve your skills for the pvp duties like Frontlines where one can pvp for reward.

I think having two players queue up via a Duty Finder just so they can duel each other for few minutes is a little to extreme and a waste of server load. Aslong as they put the 3 points that I have featured in my post, I think dueling can work. I dont understand why people are against dueling, if they themself are not going to use it. I have also seen people complain that adding dueling would be a waste of rescourses, but as majority of the players already know, there is a PvP team focusing on only adding PvP content. So I dont understand how adding dueling would interfer with the raid team adding more endgame raiding content?

But, before we start thinking about adding dueling. How about we ask the developers to fix the current pvp that we have. Right now a queue takes around a hour for someone to get into a match, that is not normal and should be a sign that something is very wrong. I think the GC restriction is the major troublemaker here. With the GC restriction we have a longer queue, because the game is grouping up and waiting for certain GC to fill up. I also find the GC restriction bad, because it blocks me from being in the same group as my friends. Forcing players who want to pvp toghter to pick the same GC, because otherwise they can not play toghter is a bad design decision and frankly, I am suprised how this was approved to be added to the game in the first place. I think making the players heroes for hire would be a better angle, this way we the players can group up with whoever we want, instead of what we have right now.

TLDR: Dueling can work, its a common thing in mmorpgs and its weird that FFXIV does not have it. It can be used for improving your skills as a pvper or do some PvP while waiting in a queue. Aslong as they give players a way to block dueling request, make certain zones only for dueling and make dueling not give any token. I dont see how it can not work.