The reason why Fire isn't considered a PvP spec in WotLK is because it doesn't have the control and survivability of Frost/Arcane or Arcane/Frost. However that's mostly because of Arena. Fire has always been usable in Battlegrounds because a talent spec is less important in Pugs than it is in a specifically orchestrated Arena Team like the ever popular Rogue/Mage/Priest.

I looked through your talent tree and made some revisions.

http://cata.wowhead.com/talent#obcG0uobhaZfVcbsbIoVuohst

Mostly I moved around first tier talents that didn't mesh well or are unnecessary.

In Arcane you chose Arcane Focus over Improved Missiles. I would argue against that because of the same reasons you've already mentioned about mana. Burst is supposed to be less important in Cataclysm but we don't have much to go on at the moment, so until we know for sure I wouldn't put a lot of importance in mana efficiency. Instead I'm going to put points into Improved Missiles so that if I'm locked out of Fire, or casting Frost Bolt, I will have more powerful missiles.

Moving down the tree.

Arcane Repulsion, this talent I changed to 1 point, and put 1 point into Focus Magic. Arcane Repulsion will surely be a nice talent but we don't really need more than 2 seconds and 4 yards do we?

As for Focus Magic, well extra crit speaks for itself doesn't it? Okay well if it doesn't than consider how useful this is coupled with Hot Streak. Besides the healer you throw this on will love you. Yeah you're fire, you want to stay stuck to a healers hip, might as well give them a reason to like you.

Arcane Mind 4 points. This isn't throw away. This isn't throw away because Int = Sp in Cataclysm. So this means more damage, and more mana, and maybe more crit but crit may no longer be effected by Int in Cataclysm so who knows. But we do know you get spellpower from Int.

On to fire.

Removed Improved Fireball for a few reasons.

One, you won't be using fireball.

If you're talented with Hot Streak, you're going to want to be using Scorch and Fire Blast for those insane instant Pyroblasts [followed by a second insane POM-PB :) ].

Two, a shorter cool down on Fire Blast is just great in PvP. And as said above more ideal for Hot Streak than Fireball.

Three Incineration = all crits, all the time. Which is again great for Hot Streak.

Okay moving down the list.

Removed the points in Burning Soul and Impact, some of those points went to Arcane Mind. Three points went into Critical Mass, because this has better synergy with Hot Streak-PB. I've never once in a pvp situation thought to myself, "Gee I wish I had taken those push back talents." Maybe I'm the only one but I've never seen them useful for PvP.

The remainder of the Fire talent points were chosen with utility in mind, and the fact that there just aren't that many opportunities outside of the Warsong Flag room or choke points in Alterac Valley to use things like flame strike. So I avoided those talents as well.

I did switch out Fiery Payback in favor of Pyromaniac because that added spell haste, that should theoretically always be up if you're dotting things, will be more useful than a reduced cast time for Pyroblast, especially if the entire talent set up is to take advantage of Hot Streak. It means you can weight your gear around needing less haste. Heck even besides that that 15% haste is just nice and less situational than Fiery Payback.

Anyway, that's my two copper. I pass the torch back to you Anonymous.