So I think you guys have a good shot at this.
Starting population was 17,000 horde and 1,000 alliance.
Factor in that probably each horde player averages around 2 alts and you really only have around 6,000 unqiue horde players. Take away inactive/casual ones and you can't be fighting more than 4,000 horde players.
Now there are already 400+ unique accounts that have rerolled into the server for alliance. Thats 10% in 24 hours. Given the steam you goes have a 1,000 unique guild members by this weekend's end shouldn't be tough (I kinda think this is where you will stabalize).
Now you will lose some but you should gain some over time as the news spreads so I figure in 2 months it wont be worse than 4:1 at any level and the alliance will be more hard core and organized so I think by Christmas the server will be a straight-up fight.