I saw in the demos that you can add a trooper with a big rotary cannon type weapon that adds a handful of extra dice for that one figure, but there were other upgrade slots on the Troopers. The AT-RT could mount an underslung rotary cannon. Were there other weapon upgrades to improve the attacks on the mooks? If it's online somewhere, link me?

There was a flamethrower, a Stormtrooper heavy blaster and a Stormtrooper rocket launcher that I saw.

From pictures I've seen the flamethrower is for the at-rt, range 1, 2 black dice. Rebel trooper rotary cannon was a z-6, range 1-3, 6 white dice. Storm trooper rocket launcher is hh-12, range 2-4, 3 black dice, cost 34 points, possibly impact 3.

Looks as if there's two weapon trooper upgrades for both Rebs and Imps - my guess would be one a high volume of shots using lots of weak dice; and the other a more heavy-hitting weapon, with a lower number of stronger dice, or using the Blast mechanic which has been mentioned, ignores cover - e.g. the AT-RT Flamethrower has this.