I'd talk to the guy first, see how he feels about it. If its something you can settle with a discussion it'd probably be the most satisfying solution for both of you. If you cant, most wins out of 3 duels?
I don't think you gave us enough information to go on. The only differences between you and him seem to be that you know some of these players IRL and that you don't play your off spec. Honestly, it sounds like a coin toss at that point.
Usually this kind of stuff needs to be adressed on your guild forums or in a chatroom on vent with all people involved. I my guild, officers think ahead, make a list of people with the best performance / highest attendance / most likely to stick with the guild and take it from there (we even had the guild vote on the issue)
You recently joined the guild, and you don't mention how long he's been in the guild. I'm going to assume that he's a recent recruit too (since anything else will hurt your chances); as such, neither of you have a greater claim over the other when it comes to the legendary.
If you both have a good attendance record, nice attitude, know how to play your class and are trustworthy, then it'll basically come down to whoever gets the embers first, or whoever the officers decide on. Essentially, it's not your choice at all. It's up to the guild as a whole (or at least the officer team).
The fact that this Druid has got the embers already seems to dictate who the officers are going to choose, or have already chosen. Bad luck, maybe you'll get Dragonwrath during MoP.
As many have mentioned, there are a lot of factors that should be taken into account when determining the quest line order within a guild. Especially now getting close to 4.3 the question needs to be asked, are you prepared to continue running FL every week to complete the staff? In a 10 man only guild, starting week one, I just got mine last week. It took me 19 weeks, and we are currently 6/7 HM. We had a mage decline working on the staff (third in line) just because he didn't want to have to continue running FL during 4.3 to farm shards or souls, potentially having to pug if the guild is too busy raiding DS. TBH I don't blame him. Just because you know other members of the guild IRL makes no difference in terms of the quest line. Has he been in the guild longer, is he reliable, does he contribute more to the guild, is he a solid player, etc. All of these things have to be taken into account.