I think that artificers should be allowed to equip and fire two rune arms, in addition to any other weapon they may be using. Since they only have to recharge, and not be reloaded, they would be less trouble to operate than two crossbows. However if an arti has inq training, they obviously should also be allowed to equip and fire two crossbows.
While on horseback.
And horses should be allowed knockdown and trample feats.