Ardat-Yakshi content. I love those space vampire-succubi femme fatales and would like to see more of them in the story, especially as anti-heroes, villains and/or syndicates! Maybe even.... playable? 
Handmaiden - I would like to see more Ardat-Yakshi content in the upcoming Mass Effect games, as the Mass Effect series was very inconsistent about the AY.
However, your interpretation of the Ardat-Yakshi is different than mine.
For me, the Ardat-Yakshi was an allegory (and a near-anagram) for Addiction and Recovery. There was a time when addicts were highly stigmatized. Their only option was to be placed in sanitariums for the rest of their lives. For those found to be AY, their only choice is to be sequestered in a Monastery or to be Executed.
An active addict is very selfish and self-centered. They are manipulative and suck the life out of everyone who cares for them. Morinth represented an addict who was fully under the control of her addiction. Like addicts who never recover, Morinth faces a grim outcome. She is either killed in her Mother's "intervention" or if Shepard "enables" her she eventually supposedly succumbs to the Reaper indoctrination process and dies a Banshee.
When 12-step programs were introduced, addicts could recover from a seemingly hopeless disease by turning their will and lives over to Higher Power, and by the constant thought for the wellbeing of others. This actually seems analogous to the Justicar moral code of conduct. In fact, I was wondering if Samara was really an AY who was able to overcome her condition through the spiritual practices and asceticism of the Justicar code. It would seem that the life of a Justicar would be the only way an AY could live a functional life. If you look at Morinth's sister Rila as an example of a recovered Ardat-Yakshi - she sacrifices herself so that her sister, mother (if she survived ME2) and Shepard can escape and takes a few Reapers with her.
I think there are a lot of untapped plot opportunities for the Ardat-Yakshi. Some of my thoughts:
- There was a secret group of AY who adopt the Justicar code as a way of recovering for their condition. They would look for other Ays and try to help them. They run into quandary when one of their member "relapses" after a charming young man helps her out of a jam. She tries to resist his advances. In a moment of weakness the AY hunger kicks in. She "relapses" with dire consequences. She decides to turn herself in. But once she is handed over to the Justicars she inadvertently reveals the secret AY "Justicar" group she was a part of. Since people see the AY as a disease to be purged, these AY Justicars are hunted down.
- A young Asari Maiden has no idea she is an AY and mistakenly kills her first lover. On top of being horrified for what she has done, an angry mob wants her executed. A sympathetic person saves her at the last minute and brings her to safety. She spends the rest of her life trying to atone for the mistake, but has the Justicars hunting her down for her crime. Kind of a spin on Les Miserables (Les Miserables-Yakshi?)
- Finally, Morinth Lives (Ardat-Yakshi Redemption):
It turns out it takes more than a Biotic Left hook, or Reaper indoctrination to take out an Ardat-Yakshi. Outlaw Morinth surrenders herself to the Justicars after hitting her bottom. The Justicars promise her a pardon from execution and will let her live in the monestary if she can help stop a mega-Ardat-Yakshi more powerful and psychopathic than Morinth ever was. This mega AY makes Hannibal Lecter look like nice person in comparison. The Justicars themselves are too scared to go after the mega AY.
Unbeknownst to Morinth - the Justicars are just using Morinth. Either the Mega Ardat-Yakshi kills Morinth, or Morinth kills the Mega Ardat-Yakshi and then the Justicars execute Morinth.
On her quest, Morinth needs to convince other people to work with her. She can either be renegade and use manipulative tactics, or paragon to use kindness, compassion, and selfless acts. Morinth's reputation precedes her and proves difficult at first. But people see her as genuinely reformed. She makes close friends for the first time in her life and shows herself to be a good and fearless leader.
In the final showdown with Mega AY, Mega AY tries to kill Morinth by melding minds with her. There is some levity because Mega AY tells Morinth: "Do you know that when one AY melds minds with another? You will feel unimaginable pleasure. I think your mind is strong enough to survive that Morinth. I want you to have that. It will change your life."
Morinth responds: "I have used that line a hundred times on my victims. Nice try."
Mega AY says: "I figured - I never get sick of telling my victims that though. Oh that's funny. But seriously - I will feel unimaginable pleasure. You - not so much. In fact, when one AY melds minds with another AY only the strongest mind will survive the other will die. Your mind is strong Morinth - but I not nearly strong enough."
Knowing she has no choice, she tries to fight the Mega AY in a battle of mind melding. She puts up a fight, but the Mega AY is too strong, Morinth realizes she has lost. As she concedes, she thinks of the new friends she made. They believe in her. She realizes they love her and she loves them. She sees into the mind of the Mega AY and realizes how similar they both are. Morinth thinks of all the lives she destroyed driven by the insane AY hunger. She knows that she and the Mega AY are the same. They were both born with the AY condition. They both let the condition consume them and control them. Unlike the Mega AY, Morinth has felt genuine love. She pities the Mega AY that she will never feel love as Morinth has felt. As she is about to lose consciousness - rather than wishing harm on the Mega AY, she wishes that her sister AY may feel love as she has. This final thought allows Morinth to win the "melding" battle.
Upon returning to the Justicars, Morinth learns of their deception. She has the choice to either allow herself to be killed as a final act of redemption, fighting back killing the Justicars in the special way that an AY can, or escape to be on the run once again.