Fire mage in MC/BWL post AQ path

[Oudeis 1]

Once AQ is release and your guild is running it, the common guideline look like all mage should go fire. But this is Vanilla, it's also common for guild to run old content to get the drop for the new players, that item that never drop, Bindings, etc..

I suppose mage are not expected to swap spec twice a week so what the deal? Do you arcane missile on everything fire immune?

[Sabre 5]

get enough spell penetration to remove the bosses fire resistance

[quasexort 4]

I'd say it really depends on your guild and how long they've been doing BWL/MC.  If you are in a new guild that is still progressing in BWL then just stay frost for AQ/BWL/MC.  If you are in that can clear BWL but it takes 2 days to complete then you might want to stay as frost until your guild can clear BWL easily.  If you are in a guild that can comfortably clear BWL then just stay fire.  Being fire spec in a guild that can comfortably clear BWL won't impact whether the raid gets cleared or not, bosses will just die maybe 10-15 seconds slower.  

Another suggestion would be to level an alt and just do BWL/MC on your alt if you don't need any loot from those raids on your mage.  I'm sure with AQ coming out more guilds will likely start gearing alts in BWL/MC.

Also spell pen won't really make a difference since a majority of the bosses are immune to fire damage.

[Xom 8]

If you have Curse of Elements up on every mob, and have the AV ring, it's okay. You're not going to be pushing the DPS meters since there are mobs that are straight immune to fire so you'll be casting untalented Frostbolt or on Clearcasting - Arcane Missiles. 

There will be Mages who stay Frost most of the time too, and if your guild has 2-3 of each spec it can be just fine once you have the 16 debuff slots. It depends on how strict your guild is on min-maxing too. You will be able to do decent damage, especially early on with the imp groups, and dog packs, Fire has the potential to get in the top 5 in the damage in the first part of MC. You will then slowly slip down the meters and even with good gear you will be unable to compete for the top spots just due to most of your spells being partially resisted, or having to cast untalented Frostbolt/AM. I did it back in retail, with the AQ40 spell-pen proc staff and AV ring and it's decent, but you do always feel like you're fighting uphill since you're so dependent on CoE and untalented spells. But yea, as other people have said, once you have the place on Farm then min-maxing isn't going to be required when you'll be alright to keep yourself Fire for the progression raids. Most guilds would rather people to spend their gold on consumables instead of respeccing for farm raids.