Looks like my Top 12 are my most important choices:
Havik: Overall fun character with good story potential as a war provocateur. Probably is in the game anyway, being a fan favorite and having some acknowledgement in MK9. Good variation potential, if they augment his abilities a little -- imagine having projectiles that take zigzag paths, body-breaking self-buffs (and/or body-breaking parries for a grappling style), and Chaos spells that inflict status effects such as reverse controls or disabling punches/kicks/block/specials. Harley Quinn's unpredictability and "gambler" specials could be an inspiration.
Fujin: He's been missing for a while, and I'd like to see him stand up as a heavenly foil to Raiden. Could have a flight-themed, wind control, and crossbow variation. Wind control could have advanced ways to manipulate the opponent across the screen.
Bo' Rai Cho: As a serious martial arts mentor, he has a lot of potential. I'd like to see him play three variations with completely different normals instead of specials: a quick and unpredictable drunken style, a powerful and hands-on sumo style, and an acrobatic staff style to give him some extended reach. Monkey flips, belly bash, and earthquake specials would go well with all three. I'd accept the puking if it were given a less cartoonish presentation... for example, if he puked on someone and it burned the opponent with sizzling acid, stunning them momentarily, instead of the slip-n'-slide animation. Even the farting might work for him if it had a good character purpose: imagine a win pose where he flops down on his fallen opponent like he's relaxing on the couch, takes a leisurely swig, then pointedly farts on them as a final insult, having totally dominated the enemy. Comic relief with a touch of real personality, rather than descending into pointless embarrassment.
Kira: Most underrated Deception character, by my account. A natural adversary to Cassie... and possible love/hate rival to Kano. Just imagine the banter and innuendo between those two, and how they would playfully stab each other in the back. She'd be the one woman that Kano has a genuine respect for, though he'd never admit it out loud. Make her like Black Widow if she were a terrorist/weapons dealer, with a parrying/grappling "Fatale" variation that basically looks like she's disassembling her opponent with concise, debilitating strikes. A "Toxic" variation could employ poisons to slow the opponent's speed or recovery time, stun, weaken, or make them take more damage. A weapons style rounds out the picture.
Kai: Handstand variation needs to happen. Sure, Kai needs a drastic overhaul in nearly all other respects, but the handstand style would be worth it. Taking his pursuit of enlightenment and "connectedness" in his previous bios as inspiration, we could maybe convert his vertical fireballs into a more "earthy" fire manipulation power, with red-hot meteors descending from heaven and bursting up from the earth. It might be encroaching on Shang Tsung's repertoire, but Shang needs to liven up his non-morphing game a bit anyway. A third variation could give Kai control of one or more molten rock balls that he levitates to do his bidding, somewhat like Viola from Soulcalibur.
Shinnok: An Elder God with infinite magic potential and Skeleton Power. Not much more needs to be said.
Daegon: By far the more interesting of the Armageddon Bros., with a long and storied history and a deep and important influence on the entire MK universe. Dual swords? Check. What if, instead of fire, he had something like the crimson laser energy that Forrest Fox wields, possibly used for traps or other forms of field control? A dragon-themed variation, with a summoned pet that swoops in from above or behind? He's just enough of a blank slate that the team could do a lot with him to make him a truly formidable demigod.
Drahmin: Too bad the developers don't like him, because a good number of people do, and he's one of MKDA's catchier designs. Imagine him going all Ong Bak on you with that giant metal club; this guy is built for knees-and-elbows action, perfect for a wild and highly motile "Unmasked" fighting style. A "Tormentor" variation centered on his club could introduce more club specials with stunning, staggering, or grounding properties, built for extending combos. A third "Unstoppable" style could include power- and recovery-enhancing taunts.
Reiko: There is something undefinable that I like about this guy. Perhaps it's that he is actually skilled in planning the movements of armies; very few MK characters act like army generals, even (especially?) the ones who have previously played that role. Where everyone else knows the Art of Kombat, Reiko specializes in the Art of War, and MKX in particular kind of needs a figure like that. While I have no idea what I'd want to see for his moves, it seems like he should be very bold, direct, efficient, and highly disciplined. None of that twirling and carnival-kicking crap, and shurikens don't seem to fit the "general" theme very well either. Personally, I'd give him a straight-up Medieval arsenal to play with.
Nitara: Flight. Blood-drinking for buffs. An enhanced melee variation with additional scythe moves. If D'vorah, why not Nitara? Along with her natural nemesis...
Ashrah: Tied with Kira for Most Underrated Deception Character on my list, and potentially a key figure in the Netherrealm events. She has such a unique female design and wields the power of "holy" light, which is a refreshing break from all the dark and horrible shit. She also has voodoo dolls, which would make an interesting variation. I could see her having a cloudlike, lighter-than-air grace to her movements.
Shujinko: Even though Kung Lao has arguably taken up the role of wizened master kung fu artist in MKX, he still doesn't match the universal kombat knowledge of Shujinko. In MKX, Shujinko would be so old, and he has literally seen it all and practiced every martial art and mastered every magic power in existence. Shujinko is a legend, sitting just this side of being a damn god, and certainly his quest for the Kamidogu would see him getting involved in these new turns of events. As the Netherkast folks pointed out in one of their early episodes, he could conceivably use the skills of other kombatants without directly ripping off their moves, incorporating them into his fighting style in a uniquely balanced moveset. His signature power, though, has always been the absorption of abilities from other kombatants -- which he could possibly use to, say, disable his opponent's specials. One possible Shujinko setup would be to give him a "Weapon Master" fighting style, a "Magic Master" style, and though it might be a bit of a reach, he could have a "randomizer" variation that randomly selects another fighting style from the roster, kind of like Tekken's Mokujin/Combot.
... The rest of the list, I'm sort of "meh" about in comparison to these, mostly because they seem limited in terms of story and/or variation potential. But honorable mentions go to Sareena, Mavado, Hotaru, and Tanya.
