Making 2nd weapon been put in acc slot would be slight unusual. So for case if some would make one or whole line of dual weapons (for low/mid/high lvl with current cap) having it as weapon used in weapon slot with changes in code to treat it as dual while PC attack be better. As if we want to go for 2nd weapon in other slot then it would be better done with offhand slot - slot we not have now and may not be so usefull aside using 2nd weapon for some time after been added.