Plenty of summons have spells & abilities that are really great and useful. Unfortunately, the summoner has no control over how they are used (some have healing abilities which would be very useful on allies). The AI isn't entirely terrible about it, but it's not great either. Particularly with non-offensive magic (just cast Ghostly Visage Rat Arcanist please).
It would be amazing if a way for summoners to control spells/abilities used by summons could be implemented; perhaps with a player tool to designate a target of the spell that works in conjunction with the Control Companion tool and voice commands.
The summoner selects a summon with the Control Companion tool. He then types out a voice command for a desired ability, i.e "/c summon cast heal" then he uses the Targeting player tool to select himself, the summon, another player, or an area. If the target is valid for the spell and if the summon selected via the Control Companion tool has the spell/ability available then the summon queues up the action.
This would be cool and a great way for summoners to show off their prowess.