That look cant be the one we will se in the movie because it just looks like a home made fan extended Pulse rifle.
I think as the movie should take place 25-30 years after Aliens than they should upgrade the look of the gun obviously(like Force Awakens will after 32 years after Return of the Jedi), and they not in prepro that much to have a final look prop from the film.Blomkamp just finished the first draft.
For the retcon/not retcon thing i think its very much important for the fans if its always topic, and we all fans knows what happend in A3 and Ressurection no matter how old a fan is and who havent seen the last two i think not a real fan.
It was mentioned it shouldnt include Ripley and Hicks and would be easier to do a stand alone spin off of course but its all started as Sigourney wanted to finish Ripleys story in a proper way and she dont wanted to continue from wher Res left that movie would made aroun 2001 there was a script but she dont wanted to do becaudlse Eart setting or who knows why...so the only way to follow up is after the Aliens/Alien 3 era which i like but i still like A3 and Res and i dont want to get retconned or multiverse..so what could be the solution makes everyone happy?