I lost six hours today playing a necromancer in Diablo IV. Looked at the clock and said, it's what time now? Haven't done that in a while and it got me thinking, what is stopping DDO from having a competitive, and more importantly, fun, summons build? DDO has much of the infrastructure already in place, there are items that enhance summons, there are feats that support it, there are epic destinies that enhance summons, and a full-blown summoner class archetype is just there begging to be developed.
A robust summoning class would need the capability of bringing into thrall multiple minions. Then, we would have to consider a player who might be able to summon other allies already in the game (such as hirelings, gold seal hirelings, werewolves, succubi, etc). This might quickly get the hamsters burning up the wheel and could contribute to lag. Testing would need to be done to make this wouldn't overwhelm instances.
Another factor some might raise is game balance. There is a perception among some that completing quests with your thralled army isn't doing it "the right way." I'm not sure how summons would provide any advantage when you drilled down into it. Would your minions clear a room any faster than a Sorcerer or Blight Caster? Greater Shout is still going to melt mobs just as fast and the bard will be racing along far faster than a summoner can keep up. A summoner won't be a game breaker, just a different way to quest.
Adding a summoner archetype would provide a new type of gameplay that would be incredibly popular among both veteran players who want to try something different and new players who want to solo. If DDO does expand into Planescape, this would be an ideal time to introduce summoners. Summoners could either exist as a Sorcerer archetype, or could be built out as a full class with different summons possible depending on thematic lore much like different pacts with Warlocks gives different abilities, feats, and SLAs.
Many (most) of the casting classes now feel the same. Draconic AOE blasting. The delivery method and primary casting stat is a coat of paint over multiple classes that mostly do the same thing. Let's shake it up! Bring the summoner into DDO.