As to the airfield restrictions at SOU regarding the A320 in the past operators such as Iberworld and Spanair have regularly used them on routes to Spain and that was in the summer so I should imagine there wouldn't be to many restrictions to Geneva especially during the winter.
Although if any future plans for EasyJet at SOU include opening up sun routes the A319 would be more of an appropriate aircraft to use.
Good luck to EasyJet at Southampton and here's hoping the future holds well for further routes ' the futures Orange' :-)