Ooh, that reminds me. I once had the idea of making a Goa'uld faction from Stargate SG-1. Many of their ships match Allegiance ships perfectly: In the series they had bombers, troop transports, and the Death Gliders -- which are quite reminiscent of interceptors. The little Goa'uld cargo ships were occasionally used as scouts in the series, and, being little cargo ships, it also makes sense for them to carry lots of mines and probes. I also had the idea of making them the stealth ships, by allowing them to mount a cloaking device which would be researched in Tac, and special miner-killing weapons. Miners themselves have no equivalent in Stargate, but on the other hand the Goa'uld loved their naquadah, so them coming up with a mining ship isn't much of a stretch, and one could be designed based on the aesthetics of their other craft. If Death Gliders are the ints there are also no figs -- but one episode showed us an old Goa'uld Needle Threader fighter, whose main attribute was that it was designed to fly through gates, while Gliders weren't -- which could translate into Allegiance as it being able to ripcord.
There are plenty of capital ships to play around with, too, and I imagine the Attack Carrier getting perked and becoming much more important -- this would be your basic Ha'tak.
And of course, the Goa'uld provide no shortage of base design ideas.
As the series implies, in gameplay their faction would have perks to mining and paydays, tough and hard-to-destroy bases, mainly energy weapons with fairly high spread and low rates of fire, but lots of damage, overall below-average ships in terms of speed, strength, and manoeuvrability, and no missiles. They'd also have slow build times, a slow ripcord time, and slow research... But, like the Belters, they'd be able to easily put to use almost any enemy technology they steal, even without the appropriate tech base.
They should also be able to build an "Iris", just because -- I wonder if this is possible without a code change: It would be a drone that, when ordered to "deploy" at an aleph, produces a simple disk-shaped structure right next to the aleph, facing towards it, that no incoming enemy ship could avoid a disorienting collision with.
Now, the other factions in the SG-1 universe would be much harder to design a faction for, since the Goa'uld have the most developed fleet. One idea might be to combine several of the "good" factions together, say, with Tau'ri fighters, some Asgard capital ships, some puddle jumpers, etc. >_>